ORGANIC COMPOUNDS - Home - StudyTime NZ · 2019. 7. 18. · Level 3 hemistr Organic Compounds Organic Compounds with just Carbon and Hydrogen With just two types of atoms, and only

NCEA | Walkthrough GuideLevel 3CHEMISTRY

ORGANIC COMPOUNDS

Introduction 4

Functional Groups 5

Organic Compounds with just Carbon and Hydrogen 5Organic Compounds with other Atoms Attached 10Acidic and Basic Organic Compounds 13The Carbonyl Group 16Acyl Chlorides 18Amides 19Ketones and Aldehydes 20Primary, Secondary and Tertiary Groups 21

Isomers 24

Structural/Constitutional Isomers 24Optical Isomers 26Chiral Carbons 28Differences between Optical Isomers 29

Organic Reactions 30

Addition Reactions 30Reaction 1: Alkene to Alkane 31Reaction 2: Alkene to Haloalkane 32Reaction 3: Alkene to Dihaloalkane 32Reaction 4: Alkene to Alcohol 33Markovnikov’s Rule 34Elimination Reactions 35Reaction 1: Alcohol to Alkene 35Reaction 2: Haloalkane to Alkene 37Reverse Markovnikov’s Rule 38

Oxidation and Reduction Reactions 39

Reaction 1: Oxidation of Primary Alcohols 39Reaction 2: Oxidation of Secondary Alcohols 41Reaction 3: Reduction of Aldehydes and Ketones 41Reaction 4: Oxidation of Alkenes 42Substitution Reactions 42Reaction 1: Haloalkane to Alcohol 43Reaction 2: Haloalkane to Amine 43Reaction 3: Alcohol to Haloalkane 44Reaction 4: Carboxylic Acid to Acyl Chloride 44Reaction 5: Acyl Chloride to Carboxylic Acid 45

Level 3 Chemistry | Organic Compounds

Reaction 6: Acyl Chloride to Amide 46Neutralisation Reactions with Carboxylic Acids 46Acid-Base Reactions involving Amines 48Condensation Reactions 49Reaction 1: Carboxylic Acid + Alcohol to Ester 49Reaction 2: Acyl Chloride + Alcohol to Ester 50Reaction 3: Acyl Chloride + Amine to Amide 51 Hydrolysis 52Triglycerides and their Hydrolysis 53Distillation, Reflux and Separating Funnels 54

Polymers, Amino Acids and Proteins 58

Polymers 58Amino Acids and Proteins 61

Properties of Organic Compounds 63

Introduction to Polarity 63Polarity of Organic Compounds 66Introduction to Melting/Boiling Point 68Melting/Boiling Point of Organic Compounds 70Introduction to Solubility 71Solubility of Organic Compounds 72

Identification Tests 74

Red and Blue Litmus Paper 74Distinguishing between Different Types of Alcohols 75Bromine Water 77

Distinguishing Aldehydes and Ketones 79

Benedict’s and Fehling’s Solution 79Tollens Reagent (Silver Mirror Test) 79Acyl Chlorides and Water 80

Key Terms 82

4 Level 3 Chemistry - Organic Compounds | © Inspiration Education Limited 2017. All rights reserved.


INTRODUCTIONThis standard is all about carbon.

Well, the name of this standard is actually “organic chemistry”, but as you’ll see, that basically means we’re dealing with carbon atoms. These versatile atoms give us stuff like alcohol, vinegar, petrol, and all sorts of handy things.

“Organic” is a term that is thrown around a lot these days: organic farming, organic foods and so on - none of which have anything to do with the organic chemistry we’re about to get stuck into. So, what does it really mean? Organic chemistry is basically the study of hydrocarbons - the carbon and hydrogen molecules that are vital to life on Earth. The molecules that we are composed of and the molecules we rely on for food and our survival are mostly organic. In fact, the DNA that encodes all our genetic information is just one big, long organic molecule!

I guess you could say that if you understand organic chemistry, you understand life…

What will you learn in this cram guide?

There’s a whopping 9 million different organic compounds, give or take a few, and you have to MEMORISE THEM ALL!

Just kidding! But we’ll begin the guide by looking at the conventions used to name all of these organic molecules, looking at things like the number of carbons they have and what other kinds of atoms they have hiding away.

From there we will look at some of the basic functional groups, how to name each one, how different functional groups are different from one another, and what kind of properties they each have.

After this we’ll go off and talk about these things called isomers and how we can identify whether two molecules are isomers.

The next section is the core of organic chemistry: the organic reactions. Often dreaded by most chemistry students, we can classify each reaction into addition, elimination, substitution, oxidation, condensation and hydrolysis reactions, and then look at the different types of reactions each functional group is involved in. By the end of it you will be able to draw up a nice flow chart showing how to use organic reactions to get from one functional group to another.

We’ll also spin a few yarns about these things called triglycerides and polymers, including amino acids and proteins. Then, we’ll end with identification tests which are ways to identify what kind of organic molecule you have in your beaker.

Level 3 Chemistry - Organic Compounds | © Inspiration Education Limited 2017. All rights reserved.5


A word on exam strategy

Organic chemistry is a MASSIVE external topic and so there is a lot to take in. But the idea is that you should be able to make links between each concept or idea, rather than thinking about everything as separate, individual topics. For example, students often just memorise the basic organic reactions without understanding why these reactions occur the way they do! So, the key is to constantly make those links.

Here at StudyTime, we’re pretty much GCs (good citizens), so to help you out, we’ve made this guide in plain English as much as we can. We’ve also included a glossary for some of the key terms that you’ll need to master for your exam.

However, the language we use isn’t always something you can directly write in yourexam. When this is the case, we offer a more scientific definition or explanation (in ahandy blue box) underneath. These boxes are trickier to understand on your first readthrough, but contain language you are allowed to write in your exam. Look out forthem to make sure you stay on target!

FUNCTIONAL GROUPSFunctional groups are the important bits of each organic molecule, and may include double or triple bonds, single atoms like halogens, or small groups of atoms like hydroxyl, carboxyl and amine groups. Sound like a bit of a heavy list?

Don’t worry! In this section, we’ll run through each functional group in more detail as well as how to name them.

So, by the end of this section you should be familiar with:

The simplest organic compounds - those with just carbon and hydrogen - and how to name them. The organic compounds with a few exciting atoms attached - haloalkanes and alcohols - and how to go about naming them. The acidic and basic organic compounds, carboxylic acids and amines respectively; what makes them acidic/basic, and what to call them. Classifying haloalkanes and alcohols.

O



Organic Compounds with just Carbon and Hydrogen

With just two types of atoms, and only single covalent bonds throughout the molecule, alkanes are the simplest, and therefore the most boring, organic compounds.

Throwing together some carbon and hydrogen atoms might not get you an alkane.

That’s because alkenes and alkynes are also made up of just carbon and hydrogen atoms

There’s just one small thing that makes alkenes and alkynes different from alkanes. Imagine the carbon atoms in the carbon chain of alkanes as colleagues, and nothing more. They’re happy with forming a covalent bond with one another, but only because they want to get the job done.

In alkenes, two of the carbon atoms are more than just colleagues, they become friends. Rather than just having a single covalent bond between them, they have 2, which is referred to as a double bond. It’s their way of getting closer to one another.

H

H

C CH

Hdouble bond

If all the carbon atoms in alkanes are just colleagues, and two carbon atoms in alkenes are friends, in alkynes two of the carbon atoms are best friends! That’s because things get a lot more close and personal with the presence of at least 1 triple carbon-carbon covalent bond.

CH HC

triple bond

Naming Alkanes:

When it comes to naming alkanes, there are two parts to their name:

1. The number of carbon atoms in the longest carbon chain determines the ‘prefix’ of the alkane name. So, if you chuck on 3 carbons atoms it would have the prefix, “prop-“. (refer to the following table if you need a refresher from last year)

2. All alkanes end with the suffix, “-ane”. Using the same example as above, an alkane with 3 carbons would be called “propane”.



Number of Carbon Atoms Prefix Alkane Example Side Group

1 Meth- Methane Methyl2 Eth- Ethane Ethyl3 Prop- Propane Propyl4 But- Butane Butyl5 Pent- Pentane Pentyl6 Hex- Hexane Hexyl7 Hept- Heptane Heptyl8 Oct- Octane Octyl9 Non- Nonane Nonyl10 Dec- Decane Decyl

H

C

H

H

C

H

H

C

H

HH propane

Naming Alkenes:

Naming alkenes is pretty standard. The thing that unites all alkenes is the suffix, “-ene”, which gets thrown on at the end of the molecule’s name.

The start of the name comes down to the number of carbon atoms in the main carbon chain, where one carbon is “meth-“, two carbon atoms is “eth-“, and so on.

In alkenes, any two of the carbon atoms can form a double covalent bond and become friends, so it’s important to say who’s getting friendly with who in the molecule name. To indicate the position of the carbon-carbon double bond, take the lowest numbered carbon of the two carbon atoms involved, and slot the number between the prefix and “-ene”.

So, if there’s a double bond between the 1st and 2nd carbon atoms in an alkene with 5 carbons, its name will be “pent-1-ene” (not pent-2-ene).

HH

C

HH

H

C

H

H

C

H

H

H

C HC

pent-1-ene



So, if there’s a double bond between the 2nd and 3rd carbon atoms in an alkene with 4 carbons, its name will be “but-2-ene” (not but-3-ene).

H

C

H

H

C C

H

H

H

C HH

but-2-ene

Naming Alkynes:

By now you’ll hopefully be getting used to naming organic compounds. Figuring out the prefix based on the number of carbon atoms in the main chain should be no problem.

When it comes to naming alkyne molecules, the suffix is “-yne”.

Just like with the double bond in alkenes, you must include the position of the triple bond, and put the number position between the prefix and “-yne”.

H C C

H

H

C H

propyne

H C C

H

H

C HC

H

H

but-1-yne

Saturated and Unsaturated Compounds

If you’ve ever had the misfortune to be lectured about your health and wellbeing you may have heard the terms “saturated” and “unsaturated” being thrown around, especially when talking about fats. Well, these terms can be used to classify many organic compounds.

In fact, all alkanes are said to be saturated

It’s not because they’re soaking wet, it’s because all carbon-carbon bonds are single bonds, and there are no carbon-carbon double or triple bonds at all.

CH

H

H

H

H

C H

ethaneCC

H

H

H

H

H

H

C HH

propane

CC

H

H

H

H

H

H

C C

H

H

HH

butaneCC

H

H

H

H

H

H

C C

H

H

C

H

H

HH

pentane



All these alkanes above have single bonds - no double or triple bonds present.

Remember, carbon atoms have 4 valence electrons so must form 4 and only 4 covalent bonds

When two carbon atoms form a double bond in alkenes they must each ditch 1 hydrogen atom to make some room. Because two hydrogen atoms were removed to make way for the friendship-forming double covalent bond, alkenes do not have only single carbon-carbon bonds, and are therefore unsaturated.

C

H

H

H

H

C

ethene

CC

H

H

HH

H

C H

propene

CC

HHH

H

C C

H

H

HH

butene

The alkenes above only have at least one double bond - not all of their covalent bonds are single ones. This is the same for alkynes as they have at least one triple carbon-carbon bond - they are also unsaturated.

Friendships may not last forever, and it turns out the second carbon-carbon bond in the double bond of alkanes, or the second and third carbon-carbon bond in alkynes, is easier to break than a standard single carbon-carbon covalent bond.

This makes alkynes and alkenes more reactive than alkanes

There’s one more thing that we need to talk about…

...often alkanes, alkenes and alkynes will have branched groups

Although we said that alkanes, alkenes and alkynes have two parts to their name, sometimes there’s an additional part. Some organic molecules have smaller carbon chains that branch off from the main one. It’s not fair to ignore them, so we give them a consolation prize for trying. These are known as side groups.

The main side groups you will be dealing with are the methyl side groups (with one branched carbon) and the ethyl side groups (with two branched carbons). Sense a bit of a pattern? The groups are named using the same prefixes that we use to name our carbon chains and they all end in “-yl”.



branched groupmethylgroup

ethylgroup

H

C

H

H

C

H

H

C

CH3

H

C

H

H

H

CH H

longest chain

H

C

H

H

C

H

H

C

HH H

H

H

C

C

H HC

H

H

CH C

H

C

H

H

H

H

longest chain

To incorporate these side chains into the name is quite straightforward. All we have to do is say where the group is and what it is. This goes at the front of the name. For example in the image above we have a methyl group on the 3rd carbon and so that molecule is called 3-methylpentane. The other molecule has an ethyl group on the 4th carbon and so it is called 4-ethylheptane.

STOP AND CHECK:

Turn your book over and see if you can remember:

How to name alkane molecules. What is meant by the terms, “saturated” and “unsaturated”. Are alkanes

saturated or unsaturated? The functional group present in alkenes. How to name alkene molecules. The functional group present in alkynes. How to name alkyne molecules.

Try to explain it in your own words.

Organic Compounds with other Atoms Attached

Some say that simplicity is the ultimate form of sophistication. That may be true, but when it comes to organic compounds, there needs to be more excitement than just carbon and hydrogen atoms. So, it’s time to mix things up!

Haloalkanes look an awful lot like alkanes, except for one little key difference: an intruder lurks within the main carbon chain. This intruder is a halogen atom.

Halogens are a special group of elements found way down in Group 17 of the Periodic Table of Elements...

...starring fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Just having this one halogen atom attached to one of the carbon atoms is a complete game



changer, altering the physical and chemical properties, making them a separate functional group.

possible halogen atomsto make a haloalkaneCC

HH

H

C

H F

I

ClBr

HH

H

Naming haloalkanes is a little trickier than with other organic compounds. Unlike with alkanes, alkenes and alkynes, the unique part of a haloalkane’s name is a prefix rather than a suffix.

Secondly, the prefix used actually depends on the what halogen atom is attached

So, if it’s fluorine it would be “fluoro-“, if it was chlorine you’d use “chloro-“, for bromine “bromo-“, and in the unlikely event that iodine is present, you’d need to use “iodo-“. This goes at the start of the name.

Next comes the part of the name which tells us how many carbon atoms are in the main chain, and it ends with “-ane”.

Because the halogen atom can go on any of the carbon atoms it’s important to also say where it is on the molecule. For example, a haloalkane with a chlorine atom attached to the 2nd carbon in a 5-carbon chain would be called “2-chloropentane”.

2 - chloropentane

e.g. CH3 CH

Cl

CH2 CH2 CH3

Sometimes we may get two halogens - either two of the same halogen atom or two different ones.

When you have two different halogen atoms you simply pile up the prefixes on top of each other, and put them in alphabetical order. For example, if there is a butane with a bromine on carbon 1 and a chlorine on carbon 2, you will have 1-bromo-2-chlorobutane (not 2-chloro-1-bromobutane). When you have two of the same halogen atoms you first list all the carbon numbers involved with bonding to these atoms, and then you use di- when there are two of the same halogen or tri- when there are three. For example, a propane chain with two chlorine atoms, both on carbon 1, would be called 1,1-dichloropropane.



1 - bromo, 2 - chlorobutane

1, 1 - dichloropropane

e.g.

e.g.

Br CH2

Cl

CH CH2 CH3

Cl

ClCH CH2 CH3

Alcohol molecules contain the hydroxyl functional group

This hydroxyl group is composed of an oxygen covalently bonded to a hydrogen atom (-OH). This -OH group can be bonded to any one of the carbon atoms in the main chain.

This little hydroxyl group does wonders, drastically changing the properties of alcohol molecules compared to other functional groups. That’s because the -OH is highly electronegative and makes small alcohol molecules polar. Don’t worry if those concepts sound a little scary right now - we’ll look into them in depth later on!

Naming Alcohol Molecules:

To name alcohol molecules we use the suffix, “-anol”, which goes at the end of the molecule’s name.

The position of the hydroxyl group must also be shown in the name, which is represented by a number. This number goes in between the “an” and the “ol” of “-anol”.

For example, an alcohol with the -OH group attached to the 2nd carbon of a 3-carbon chain is called “propan-2-ol”.

propan - 2 - ol

hydroxyl (-OH) groupCH3

OH

CH CH3

Why stop at just 1 hydroxyl group, why not add another one for the yarns?

Alcohol molecules with 2 hydroxyl (-OH) groups attached to the main chain are called diols

Not a whole lot changes and they still act the same as normal alcohol molecules.

The real fun comes in their naming



The first part of the name is the name of the alkane which would form from the diol’s main carbon chain.

The second part of the name is the suffix, “-diol”.

A diol with an -OH group on the 1st and 2nd carbon of a 3-carbon chain would be called, “propan-1,2-diol”.

propane - 1, 2 - diolCH3

OH OH

CH CH2

Stop and Check:


Where the halogen atoms are found on the Periodic Table. The common halogen atoms. The prefixes used for haloalkanes containing:

• Fluorine• Chlorine• Bromine• Iodine

The name of the functional group in alcohols. The atoms that make up the functional group of alcohols. How to name alcohol molecules. The structure of a diol – what’s the difference between an alcohol and a diol. How to name diol molecules.


Acidic and Basic Organic Compounds

So far all our organic compounds have been pretty boring considering they are all neutral in solution. Carboxylic acids change this!

Carboxylic acids are, as their name suggests, acidic

These organic compounds contain an acidic functional group, the carboxyl (-COOH) group, making them acidic. In a carboxylic acid, the end carbon in the main chain is covalently bonded to two oxygen atoms, one with a double bond and one to an OH group - this represents the carboxyl group.



To make sure we’re all on the same page:

Acids are defined as proton donors

When an acid is in water, it releases a hydrogen ion (H+), equivalent to a proton.

In carboxylic acids, the hydrogen ion comes off from the carboxyl group - the hydrogen atom that’s on the hydroxyl (-OH) group. When the hydrogen is removed from the carboxyl group, it leaves behind the carboxylate group: COO−.

CH3 + H

++

HCH2 O

O

O H

OC

CH3 CH2O– H

O H HC

(H2O / water)

(H3O+ / hydronium ion)

proton (H+) is donated

With carboxylic acids being the only acidic organic compound in Level 3 Chemistry, it is only fair to have a basic one as well.

Amines contain an −NH2 group attached to one of the carbon atoms in the main carbon chain

The main property of amines is that they are basic

To make sure we’re all on the same page, bases are defined as proton acceptors, where the base receives a hydrogen ion (H+), or proton, from an acid. If you need a bit of revision, head over to the Level 3 Aqueous Systems guide.

In amines, the hydrogen ion attaches to the nitrogen forming NH3+ which is attached

to one of the carbon atoms.

CH2 + H

++ -

HCH3 CH2 O

HO

H

HN

CH2CH3 HCH2

H

HN

(H2O / water)

(OH– / hydroxide ion)

proton (H+) is accepted



Naming Carboxylic Acids and Amines:

To name a carboxylic acid you must count the number of carbon atoms in the main chain, just like you have been. This gives the prefix of the molecule’s name.

Carboxylic acids end with “-anoic acid”

However, unlike other functional groups, the carboxyl group can only be attached to the 1st carbon atom in the main chain. Therefore, we don’t need to indicate its position.

For example, a carboxylic acid with a 4-carbon chain would be called “butanoic acid”.

butanoic acidCH3 CH2 OH

OCH2 C

4 3 2 1

This position of the carboxyl group is important. Even when other functional groups are present, the carboxyl group is ALWAYS on the first carbon, and it trumps all other functional groups. So start numbering the carbon atoms in the chain from here.

For example, if there is 3-carbon chain with a bromine on one end and a carboxyl group on the other, the molecule will be called 3-bromopropanoic acid. You must always start numbering from the carboxyl group.

3 - bromopropanoic acidBr CH2 OH

OCH2 C

3 2 1

When it comes to naming amines you can either use the prefix, “amino-“, or the suffix, “-amine”

By now you should know that you must indicate which number carbon atom the amine group is attached to.

For example, an amine with the -NH2 attached to the 1st carbon of a 3-carbon chain may be named “propan-1-amine” or as “1-aminopropane”.

Either is acceptable, although sometimes you may be forced to use one or the other depending on other functional groups present. However, using it in the beginning is always fine, so if in doubt just use that one. And, if they give you an example of an amine in the exam it will be written both ways so you shouldn’t get confused!

propan-1-amine or 1-aminopropaneCH3 CH2 CH2 NH2

3 2 1



STOP AND CHECK:


The atoms which make the carboxyl group. How to name carboxylic acid molecules. Why it is not necessary to the indicate the position of the carboxyl group in

carboxylic acid molecules. Why the carboxyl (-COOH) functional group is said to have acidic properties. What atoms make up the amine group. The prefix and suffix that can be used to name amines. Why the amine (-NH2) group has basic properties.


The Carbonyl Group

All of the new functional groups in Level 3 contain a common group called the carbonyl group. This is a functional group that is made up of a carbon atom attached to an oxygen with a double covalent bond (C = O):

RC

O

Rʼ

The thing that changes between these different organic compounds with a carbonyl group is that the R and/or R’ changes. There are 5 new functional groups to cover:

1. Esters2. Acyl chlorides3. Amides4. Aldehydes 5. Ketones

You may have noticed that we have already come across a carbonyl group with carboxylic acids.

Esters:

Imagine an alcohol molecule driving down the road at full speed with a carboxylic acid molecule speeding in the opposite direction. Now imagine they crash head-on. The resulting mangled mess would be an ester.



That’s because esters look like a carboxylic acid with an alcohol jammed on the end

The -OH group attached to the carboxylic acid is removed, and the carboxylic acid and alcohol are attached to one another through the oxygen atom of the -OH group on the alcohol, after a hydrogen atom has been removed.

The impact of the crash throws out an H2O molecule as a waste product.

C

H

H

H

C

H O

O H

H2O

H

CC

H

H

H

C

H

H

O H C

H

H

C

H

H

H

C

H

H

H

C

H O

OH

C

propanoic acid + ethanolester linkethyl propane + ethanol

++

Naming esters can be a bit confusing to start with

There are two main parts to its name:

1. One part represents the alcohol (“-yl”).2. One part represents the carboxylic acid (“-anoate”).

In front of the “-yl” is the number of carbon atoms in the main chain of the alcohol, while the number of carbon atoms in the main chain of the carboxylic acid goes in front of the “-anoate”.

So, if a two-carbon alcohol and a three-carbon carboxylic acid are used to produce an ester, the ester will be called “ethyl propanoate”.

CH

H

CH

H

H

CH

H

H

CH O

OH

C

carboxylic acid partalcohol part

STOP AND CHECK:


The name of the functional group in esters. The two organic compounds that are used to make esters.



How to name ester molecules.


Acyl Chlorides:

Sometimes they’re called acid chlorides - so watch out for that!

Acyl chlorides are actually derived from carboxylic acids

This is because the carbon atom attached to the chlorine is also attached to an oxygen atom through a double covalent bond (C=O).

Basically, the -OH part of the carboxyl group (-COOH) group in carboxylic acids has been replaced by a -Cl to produce the acyl chloride.

When it comes to naming acyl chlorides, slap on “-anoyl chloride” at the end of the name

Because the carbon atom forms 3 covalent bonds in total with the chlorine and oxygen atom, it only has room to bond to one other carbon atom.

This means that, luckily for us, the -COCl functional group can only ever be on the 1st carbon atom, exactly like carboxylic acids.

An acyl chloride with a 3-carbon chain would be called propanoyl chloride:

acryl chloride group

propanoyl chloride

CH3 CH2 Cl

OC

STOP AND CHECK:


The name of the functional group in acyl chlorides. How acyl chlorides are related to carboxylic acids. How to name acyl chloride molecules.




Amides:

Amides look an awful lot like amines, but they are actually another derivative of carboxylic acids.

Remember how the -OH from the carboxyl group (-COOH) in carboxylic acid was replaced with a -Cl to produce acyl chlorides? Well to make an amide, the -OH group from the carboxyl group is replaced with an amine (-NH2) group, producing the -CONH2 amide group.

But a good way to remember the functional group of amides is to think that an of an amine with an added double-bonded oxygen atom.

Although they look kinda like amines, amides are not bases

You don’t need to know the exact reason as it is beyond what you need to know for exams, but basically the oxygen prevents nitrogen from acting as a base and accepting protons.

Now, back to the naming amides.

Chuck on “-amide” at the end of the molecule’s name when you’re naming an amide

So, if you had an amide with a 3-carbon chain you’d get “propanamide”.

amide group

propanamide

CH3 CH2 NH2

OC

3 2 1

Since the carbon atom with the amide group has already used up 3 covalent bonds to bond to the -NH2 group and oxygen atom, it only has 1 covalent bond left.

This means that the functional group in amides (-CONH2) can only ever be on the 1st carbon atom exactly like carboxylic acids and acyl chlorides.

STOP AND CHECK:


The name of the functional group in amides.



How amides are related to carboxylic acids. How to name amide molecules.


Ketones and Aldehydes:

Aldehydes and ketones are two peas in a pod.

Both have the same functional group: a carbon atom in the main chain bonded to an oxygen atom through a double covalent bond (C = O).

But aldehydes and ketones are two different organic compounds.

The difference between them lies in the position of this C = O group:

In aldehydes, the C = O group is at the very end of the organic molecule, on the 1st

carbon in the chain. So, HO

H

H

C CH

C

would be an aldehyde.

When it comes to ketones, the C=O group can be anywhere in the main chain except

for on the 1st carbon atom. For example, H

H

H

C

O

C

H

H

C H would be a ketone.

To name aldehydes you must use the suffix, “-anal”

Thankfully because the carbonyl group is always on the first carbon atom, its position does not need to be stated in the name of the molecule.

For ketones, we use the suffix, “anone”

Since the carbonyl group can be anywhere along the carbon chain, the position number of the carbonyl group is put between the “an” and the “one” of “anone”.

For example, a five-carbon ketone with the C=O group on the 2nd carbon would be called pentan-2-one. Whereas a five-carbon aldehyde would be pentanal.

H



ketone groupaldehyde group

pentanal pentan - 2 - one

H C

O

CH2 CH2 CH2 CH3

43 521

CH3

O

C CH2 CH2 CH3

43 521

STOP AND CHECK:


The functional group in both aldehydes and ketones. The difference between an aldehyde and a ketone. How to name an aldehyde. How to name a ketone.


Primary, Secondary and Tertiary Groups

Now that we’ve met each of the different functional groups associated with organic molecules, let’s go one classification further - and look at how haloalkanes and alcohols can be classified into ‘Primary’, ‘Secondary’ and ‘Tertiary’ molecules. You may remember this from last year and it’s exactly the same this year...but let’s review.

These words are just a fancy way of saying “1, 2, 3”

Starting with haloalkanes, primary haloalkanes are molecules where the halogen atom is bonded to a carbon atom which is then bonded to just 1 other carbon atom. With secondary haloalkanes this carbon atom is bonded to 2 other carbon atoms, and with tertiary haloalkanes this carbon atom is bonded to 3 other carbon atoms.

The classification is important because it changes the properties of the molecule slightly.

primary haloalkane

CH3 CH2 CH2 Cl1

secondary haloalkane

CH3 CH CH3

Cl1 2

tertiary haloalkane

CH3

CH3

C CH3

Cl1 2

3



Just like haloalkanes, alcohols can be classified as primary, secondary and tertiary alcohols, depending on how many carbon atoms the carbon attached to the -OH group is bonded to.

primary alcohol

CH3 CH2 CH2 OH1

secondary alcohol

CH3 CH CH3

OH1 2

tertiary alcohol

CH3

CH3

C CH3

OH1 2

3

When it comes to primary, secondary and tertiary alcohols, there are some very important differences in properties that you need to be aware of. For now, be familiar with the classification - and we’ll introduce some important properties of them when we get into reactions later on!

STOP AND CHECK:


What are primary, secondary and tertiary haloalkanes? What is the difference between them?


Quick Questions

Have a go at drawing the following organic molecules:

Pentan-3-one 4-aminobutanoic acid 2-chloro-3,3-dibromo-hex-1-ene Butanamide 2,2-dimethyl-hexanoic acid 3-chloro-pentanal 1-amino-butan-2-ol Propyl propanoate 3-ethyl-pentan-3-ol 2-hydroxy-ethanoyl chloride

?



Now have a go at naming the following organic molecules:

CH3 − CH3 − CH − CH3 − Cl

OH

CH2 − CH2 − NH2

OH

Cl − CH2 − CH2 − C − NH2

O

HO − CH2 − CH2 − C − NH2

O

CH3 − C − O − CH2 − CH3

O

H − C − OH

O

CH3 − CH − CH3

CH2

CH3

CH3 − CH − C − CH2 − Cl

CH2

CH3

O

CH2 − CH − C − Cl

Cl Cl O

CH2 − C − O − CH2

O

CH3 − CH2

CH3 − CH2

CH2

Br − CH2 − CH − CH − CH2 − CH − CH3

OH

H3C − C − CH2 − C − CH2 − CH2 − NH2

OCH3

CH3



ISOMERSOrganic molecules are formed when different atoms come together and form covalent bonds. Sometimes, we can end up with some very similar looking molecules that aren’t quite identical. This happens when the same number and type of atoms come together to form a different molecule by changing up the way they bond to one another.

Basically, you start off with the same ingredients - but can get a range of different outcomes.

These different outcomes are known as isomers

It’s best to define isomers as “organic molecules with the same molecular formula (same number and type of atoms) but a different chemical structure”.

There are 3 main classes of isomers:

1. Structural (Constitutional) Isomers2. Geometric (cis-trans) Isomers3. Optical Isomers (enantiomers)

Thankfully for you, geometric isomers are not assessed this year like they were in Level 2. But, we’ll recap structural isomers before jumping into looking at optical isomers.

Structural/Constitutional Isomers

Structural isomers (also commonly known as constitutional isomers) are isomers which have the same molecular formula but a different structural formula

So, the same number and type of atoms as one another, but these atoms are bonded differently.

Structural isomers can be grouped into 3 different types:

1. Positional Isomers

These are structural isomers where the position of a functional group or a side chain is different. When functional groups or side chains are moved, and placed on a different carbon atom in the main chain, the structural formula becomes different.

For example, propan-1-ol and propan-2-ol are positional isomers as the hydroxyl (-OH) group is on the 1st carbon atom in propan-1-ol but on the 2nd carbon atom in propan-2-ol.



propan-1-ol propan-2-ol

CH3 CH CH3

OH

CH2 CH3 CH3

OH

1 2 3 1 2 3

2. Branched Chain Isomers

These are structural isomers where the main carbon chain is of a different length due to the formation of side chains, such as methyl or ethyl groups. As side chains are added, or as side chain lengths are increased, the length of the main chain decreases to keep the number and type of atoms the same in all isomers.

For example, butane and methylpropane are chain isomers. Butane has 4 carbons in its main chain, while methylpropane has 3 carbons in its main chain. However, methylpropane has a methyl group on the 2nd carbon, giving it 4 carbons (and 10 hydrogens) in total – the same as butane.

4 carbons, 10 hydrogens

butane methyl-propane

methyl group


CH3 CH CH3

CH3

CH3 CH2 CH2

1

CH3

42 3 1 2 3

3. Functional Group Isomers

Functional group isomers are an interesting type of structural isomer that do not occur that often in Level 3 Chemistry. These are structural isomers where the same number and type of atoms have been arranged in such a way that different functional groups have been formed.

For example, butene and cyclobutane are functional group isomers.

Butene is an alkene with 4 carbon atoms in its main chain, with a double bond occurring between two of the carbon atoms. This leaves 8 hydrogen atoms attached.In cyclobutane, the 4 carbon atoms form a ring structure where the first and last carbon atoms are bonded to one another. With every carbon bonded to two carbon atoms, there are two bonds available for hydrogen atoms, giving cyclobutane 8 hydrogen atoms in total. Both butene and cyclobutane have the same molecular formula (C4H8) but each has a different functional group (butene is an alkene, while cyclobutane is a cycloalkane).




but - 2 - ene cyclobutanedouble bond


H HH

HHH

H

HCH3 CH

C

CCC

CH1 3

4

2

CH3

42 3

If you are unsure of whether you have drawn a correct, or different, isomer just give it a name and see if it really is different from what you have drawn so far!

STOP AND CHECK:


What structural isomers are. The differences and similarities between positional isomers, branched chain

isomers and functional group isomers.


Optical Isomers

Optical isomers (who also have the exciting nickname of “enantiomers”) try to be a bit like geometric isomers in that they are also molecules with the same molecular and structural formula, but differ in their 3-dimensional orientation of atoms in space.

Nobody wants to be a copycat, so optical isomers can’t look too similar. While geometric isomers differ in the orientation of atoms or groups around a carbon-carbon double bond…

…optical isomers are mirror images of one another

mirror

CH

NH2CH3 CH2

CH3

CH

NH2CH3 C2

CH3

But not all molecules can exist as optical isomers

Sometimes you can rotate the ‘mirror image’ to get the original molecule, which means they’re not isomers after all.



mirror Same conformation

Original mirror image

FCl

Cl

H

FCl

Cl

H

FCl

Cl

H

180° rotation

Can be superimposed

This means that optical isomers also have to be non-superimposable

This scary-sounding word just means that you can’t place optical isomers on top of one another and get the same molecule.

Look at your left and right hands – hopefully they are mirror images of one another.

Left Right

Try stack one over the other so that they are in the exact same conformation

…it’s not possible!

Because of this, your left and right hands are said to be mirror images which are non-superimposable. If they were chemical molecules they would be optical isomers.

Pinky Thumb Pinky

Palm down Palm down

Palm down Palm up

Pinky

Thumbs and pinkies align but one hand is “Palm up” and the other is “Palm down”

Thumb Pinky Thumb



STOP AND CHECK:


How optical isomers differ from one another. What is meant by the terms “superimposable” and “non-superimposable”. Why hands are a good analogy for optical isomers.


Chiral Carbons

If you wanted to be able to form optical isomers you would just need to do one thing: get yourself a chiral carbon.

Chiral carbons are carbon atoms that are bonded to four different atoms or groups of atoms.

With just one chiral carbon a molecule will gain the ability to form optical isomers.

Chiral carbon

only 3 different groups, therefore,not a chiral carbon

CH3 CH3CH2 C

H

NH2

1

3

4

2

CH3 CH3C

H

NH2

1

3

2

STOP AND CHECK:


What makes a carbon chiral? Why chiral carbons are important in optical isomers.




Differences between Optical Isomers

Prepare to have your mind blown…

The only property that differs between optical isomers is the direction in which they rotate plane-polarised light

One optical isomer will rotate plane-polarised light in one direction, while the other will rotate it in the opposite direction.

plane-polarised light rotation of light

CH

NH2CH3 CH3

CH3

CHNH2

CH3 CH3

CH3

STOP AND CHECK:


The difference in properties of two optical isomers.


Quick Questions

Glycine and alanine are two simple amino acids - notice how they have an amine at one end (the left end in both cases) and a carboxylic acid at the other (the right end in both cases).

H2N − C − C− OH

H

H O

H2N − CH − C− OH

CH3

O

glycine alanine

Explain why alanine can exist as optical isomers (enantiomers), whereas glycine cannot

?



ORGANIC REACTIONSOrganic chemistry loves to classify stuff, and when it comes to organic reactions this is no exception. If you didn’t have enough to learn, these reaction types are important because you might be required to state what kind of reaction has taken place, or simply define each type and compare between them.

There are 7 main types of organic reactions:

1. Addition reactions2. Elimination reactions3. Oxidation and Reduction reactions4. Substitution reactions5. Acid-Base reactions6. Condensation reactions7. Hydrolysis

For addition and elimination reactions there are sometimes two possible products, and for these it’s important to take into account Markovnikov’s Rule, which we will cover in due time, don’t worry!

But, the most important part of this section (and ultimately the most important part of this external standard) are all the specific organic reactions involving the functional groups we have covered! For each of the 7 main types of organic reactions we will cover the reactions that you will need to know, including any reagents and reaction conditions required.

Addition Reactions

Okay, these reaction types are as straightforward as they sound – trust me, there’s no hidden complexities hiding beneath the surface.

Addition reactions just involve adding on new atoms to the original molecule

So it’s easy to identify if an addition reaction has occurred, because you’ll end up with more atoms on your molecule.

The only way carbon atoms can get more atoms attached to them is if they break some of their current bonds.



In addition reactions, the double or triple carbon-carbon bonds are first broken to make some room

In NCEA we really only deal with addition to double bonds because addition to triple bonds (in alkynes) can get messy pretty quickly. But just know all the same rules apply if you were to do this with alkynes.

chloroethane

e.g. CH2 = CH2 + HCl

Cl - CH2 - CH3

Cl - CH2 - CH3

CH2 CH2 CH2 H Cl+CH2 CH2 CH2double bound

breaksH and Cl atoms

are added

Although addition reactions only involve alkenes, there are 4 addition reactions you need to be aware of

The difference between them is the reagent that is added and the type of organic molecule produced as the product.

Reaction 1: Alkene to Alkane

The first addition reaction involves converting an alkene to an alkane. The difference between alkenes and alkanes is the presence of a double bond in the alkene. In order for a double bond to be formed between two carbon atoms, alkenes must have 2 less hydrogen atoms than alkanes of the same chain length.

4 carbons,10 hydrogens

4 carbons,8 hydrogens CH

H

HCH

HCH

HCH

HH

CHH

HCH

CH

CH

H+H2

HCHH

HCH

CH

CH

HH



This means that if we want to convert an alkene to an alkane we need to add two hydrogen atoms. So, the reagent we’ll use is H2, which is how hydrogen gas exists normally. After breaking the double bond, one hydrogen bonds to the each of the carbon atoms previously involved in the double bond.

But, this reaction isn’t that willing to go ahead. We need to give it a bit of a push in the right direction with a catalyst. Remember, catalysts are those things that speed up reactions by lowering the activation energy. For the addition of H2 to alkenes either a platinum (Pt) or nickel (Ni) catalyst can be used. Since they are catalysts they won’t be used up in the reaction.

Using ethene as an example, the overall reaction looks like: CH2= CH2 + H2 → CH3- CH3

Reaction 2: Alkene to Haloalkane

The difference between alkenes and haloalkanes is that alkenes are unsaturated with a double bond, while haloalkanes are saturated and contain a halogen atom attached somewhere on the main carbon chain. When the double bond breaks between two carbon atoms in an alkene, both carbon atoms need to bond to one more atom to give them a full valence shell. To make a haloalkane, one of these carbons will be given a halogen atom (such as chlorine or bromine), while the other is given a hydrogen atom.

The two possible reagents that can be used in this equation are HCl or HBr. These molecules split into the hydrogen atom and the halogen atom (chlorine or bromine), and both are added to the carbon chain.

Using ethene as an example, the overall reaction looks like either:

CH2 = CH2 + HCl → CH3-CH2-ClCH2 = CH2 + HBr → CH3-CH2-Br

There are two carbon atoms in this reaction that need additional atoms added to them after the double bond breaks. How do you choose which one gets the halogen atom and which one gets the hydrogen? For this we will need to use Markovnikov’s Rule, covered after “Addition Reactions”.

Reaction 3: Alkene to Dihaloalkane

This reaction is very similar to the last one we encountered. Rather than making a haloalkane with just one halogen atom attached, it is possible to make a dihaloalkane with two halogens. This means that, rather than using a hydrogen halide as a reagent (HCl or HBr), we use two halogen atoms.

Pt/Ni catalyst



Chlorine and bromine both exist as molecules: Cl2 and Br2. Cl2 splits into two chlorine atoms, or Br2 splits into two bromine atoms, and each one attaches to either of the carbon atoms previously involved in the double bond in the alkene.

Using ethene as an example, the overall reaction looks like either:

CH2 = CH2 + Cl2 → Cl-CH2-CH2-ClCH2 = CH2 + Br2 → Br-CH2-CH2-Br

Reaction 4: Alkene to Alcohol

Another addition reaction is the conversion of an alkene to an alcohol. Like all the reactions before now, it’s important to think how these functional groups are different: an alkene is composed of carbon and hydrogen atoms with a double bond between two of the carbon atoms; an alcohol is composed of a chain of carbon and hydrogen atoms, with a hydroxyl (-OH) group attached to one of the carbon atoms in the main chain.

Immediately, we know that somehow we need to get an -OH involved. When the double bond breaks between the two neighbouring carbon atoms, one of the carbons will get the hydroxyl group, while the other can get a stock standard hydrogen atom. Therefore, the reagent to use in this addition reaction is water (H2O)!

However, normal water won’t cut it.

Instead, acidified water (H2O/H+) is added to the alkene. The mixture is also heated.

Using ethene as an example, the overall reaction is: CH2=CH2 + H2O/H+ → CH3-CH2-OH

Just like with the alkene → haloalkane reactions, we run into the issue of deciding which carbon to give the hydroxyl group and which one to give the hydrogen atom. Again, we will need to use Markovnikov’s Rule, covered after “Addition Reactions”.

Summary

All addition reactions involve alkene molecules. They are addition reactions because the double bond is removed and new atoms or functional groups are bonded to the carbon atoms to fill their valence shell. These “new” atoms or functional groups come from the particular reagent added. The following reagents can be used with alkenes:

1. Hydrogen gas (H2) with Pt or Ni catalyst to produce an alkane.2. HCl or HBr to produce a haloalkane (a chloroalkane or a bromoalkane). 3. Chlorine (Cl2) or bromine (Br2) to produce a dihaloalkane. 4. Acidified water (H2O/H+) to produce an alcohol.



If you are given the reagent to add to an alkene and asked for the product, just think what functional group can be added to the carbon chain from the reagent.

If you are given the product and asked for the reagent, just think how this product’s functional group differs from an alkene: what atoms are missing?

STOP AND CHECK:


The definition for an addition reaction. What kinds of molecules can take part in addition reactions. Other than a polymer, the possible organic molecules that can be produced

from alkene addition reactions. The possible reagents that can be used in alkene addition reactions.


Markovnikov’s RuleWhen an asymmetrical alkene (different number and/or type of atoms on either side of the double bond) is involved in an addition reaction there can be two different compounds produced. We call these the major and minor products, where the major product is produced in greater amounts. Two products are made because if the hydrogen atom is placed on one of the carbons it produces a completely different molecule than if it was placed on the neighbouring carbon instead.

When it comes to addition reactions you need to use Markovnikov’s Rule

This rule states that the hydrogen atom is added to the carbon with the highest number of hydrogen atoms already attached. To help you remember this rule, think “the rich get richer”.

Using the alkene to haloalkane reaction as an example, there can sometimes be two possible products formed:

There are two possibilities where the H and Cl atomscan be added

the H is added to the Carbon with the

least number of H atoms

already attachedminor product major product

CH3 + HClCH

CH

H

CH3 CH

CH

H ClH CH3 C

HCH

Cl HH

CH3 + HClCH

CH

H

C... CH Cl C... C H Cl

The H is added tothe carbon with

the most H atoms already attached



Make sure you name both products, as you might find they are actually the same molecule (the same name). This is because only one product is formed in addition reactions involving symmetrical alkanes.

STOP AND CHECK:


What is meant by the phrase “the rich get richer”, in terms of addition reactions. What is the difference between the major and minor product.


Elimination Reactions

In elimination reactions, atoms are removed from two neighbouring carbon atoms in the main chain

Once this has been done, the carbon atoms have a bit of a problem: they no longer have full valence shells, as they no longer have four bonds formed.

When atoms are removed, Carbon atoms need to bond with one another and form double (or even triple) bonds.

e.g. CH3 CH2 CH2 CH2

H and Cl atoms are removedfrom the molecule

a double bond is formed instead

the carbon atoms no longer have full valence shells

Clheat

KOH(alc)+ HCl+

H C

H

C

H

H ClCl H C

Cl

H

+ H

C

H

ClC

Cl

H

H

H

H+ H

C

Elimination reactions are the opposite of addition reactions...

...so it would seem logical that if alkenes are the reactants in all addition reactions, then alkenes are the products in all elimination reactions. That’s because elimination reactions involve the formation of a double bond after the removal of atoms or functional groups from two neighbouring carbon atoms.

Alkenes can be made from two types of organic molecules: alcohols and haloalkanes.

Reaction 1: Alcohol to Alkene

Remember that, to produce an alcohol from an alkene in an addition reaction, acidified water was added to provide the hydrogen atom and hydroxyl group needed.



To go backwards, and convert an alcohol to an alkene, a hydrogen atom and a hydroxyl group need to be removed so that the double bond can be reformed

When you are thirsty, you are dehydrated because you don’t have enough water. In chemistry, there are certain substances that act as dehydrating agents that remove water.

One of these is concentrated sulfuric acid (H2SO4) and can be use to remove the equivalent of a water molecule (H + OH) in the elimination reaction, converting an alcohol to an alkene. Once the hydrogen atom and hydroxyl group are removed from the alcohol they combine to form water. The carbon atoms they were originally bonded to need to refill their valence shells, so instead form a double bond with one another.

Using ethanol as an example, the overall reaction looks like: CH3-CH2-OH → CH2 = CH2

In the addition of acidified water to alkenes, we were worried about which carbon atom to add the hydrogen to and which one to add the hydroxyl group to. In this reaction there is only one carbon that will have the hydroxyl group (-OH) attached. In terms of where we take the H from, there are often a few possible options.

The hydrogen atom has to be taken from a carbon next door to the OH group

This influences where in the chain the double bond forms, and therefore influences the particular alkene produced.

OPTION 1

remove hydrogenfrom carbon 1

but - 1 - ene but - 2 - ene

H HCH

HCH

OHCH

HCH

H

H HC

H

HC

H

OHC

H

HC

H

HH HC

H

HC

H

OHC

H

HC

H

H

OPTION 2


HCH

CH

CH

HHCH

HH HC

H

HCH

CH

CH

H

A similar rule to Markovnikov’s Rule - “Reverse Markovnikov’s” rule (also sometimes called Saytseff’s rule) - is used to determine which product is most likely to form (and therefore be formed in greater amounts). For now, just become familiar with how the reaction works - and we’ll cover this rule after “Elimination Reactions”.

conc. H2SO4



Reaction 2: Haloalkane to Alkene

Remember that, to produce a haloalkane from an alkene in an addition reaction, either HCl or HBr was added to provide the hydrogen atom and halogen needed.

To go backwards, and convert a haloalkane to an alkene, a hydrogen atom and the halogen (either Cl or Br) need to be removed so that the double bond can be reformed.

Unfortunately, it’s not obvious what the reagent will be: alcoholic potassium hydroxide (KOH(alc)) is used. The reaction also requires heat.

Be very careful of the state of this reagent. It isn’t any old potassium hydroxide, and especially isn’t aqueous potassium hydroxide, it is potassium hydroxide dissolved in alcohol, producing alcoholic potassium hydroxide. This is shown using the “alc” symbol: KOH(alc).

Aqueous potassium hydroxide (KOH(aq)) is a similar reagent but is used later on in a different organic reaction. Do not get confused here, remember - alcohol eliminates.

When the hydrogen and halogen atom are removed from the haloalkane they combine to form either hydrogen chloride (HCl) or hydrogen bromide (HBr), depending on the halogen atom.

Using bromoethane and chloroethane as examples, the overall reaction will look like either:

CH3-CH2-Br → CH2 = CH2 + HBr

CH3-CH2-Cl → CH2 = CH2 + HCl

Just like with the elimination reaction involving alcohols, there’s the issue of which carbon atom to remove the hydrogen from

A similar rule to Markovnikov’s Rule - “Reverse Markovnikov’s Rule” - is used to determine which product is most likely to form (and therefore be formed in greater amounts). This will be covered after “Elimination Reactions”.

Summary

All elimination reactions produce alkene molecules. They are elimination reactions because the double bond is formed after atoms or functional groups are removed from neighbouring carbon atoms. These removed atoms or functional groups combine to produce side products.

KOH(alc)

KOH(alc)



The following reagents can be used to produce alkenes in elimination reactions:

1. conc. H2SO4 is a dehydrating agent used to convert alcohols to alkenes. 2. KOH(alc) + heat is used to convert haloalkanes to alkenes.

STOP AND CHECK:


The definition for an elimination reaction. What kinds of molecules can take part in elimination reactions. The product of all elimination reactions. The reagents used and side products formed in the elimination of alcohol

and haloalkanes.


Reverse Markovnikov’s Rule

When it comes to elimination reactions we sometimes need to use what is referred to as “Reverse Markovnikov’s Rule”.

For some elimination reactions involving alkanes, there are two possible pairs of carbon atoms the double bond can form between

Say we remove a halogen/hydroxyl from the 2nd carbon, we can either remove the hydrogen from the 1st carbon or from the 3rd carbon. This influences where the double bond will be formed and therefore influences what product is made!

OPTION 1


but - 1 - ene but - 2 - ene

H HCH

HCH

OHCH

HCH

H

H HC

H

HC

H

OHC

H

HC

H

HH HC

H

HC

H

OHC

H

HC

H

H

OPTION 2


HCH

CH

CH

HHCH

HH HC

H

HCH

CH

CH

H



So, when an elimination reaction occurs, a hydrogen is always removed from one of the carbons adjacent to the functional group (e.g. hydroxyl/halogen) but when the molecule isn't symmetrical there is major and minor product. In this case the major product is the one where the hydrogen atom is removed from the carbon with the least number of hydrogen atoms already attached.

To help you remember this rule, think “the poor get poorer”.

There are two times when you will use Reverse Markovnikov's Rule:

1. Alcohol to alkene2. Haloalkane to alkene

STOP AND CHECK:


The two times when you will need to use Reverse Markovnikov’s Rule. What is meant by the phrase “the poor get poorer”, in terms of

elimination reactions. What is the difference between the major and minor product.


OXIDATION AND REDUCTION REACTIONSOxidation can be thought of as gaining oxygen bonds

If you did the Level 2 or 3 Chemistry Redox internal you had another definition for oxidation, but, for now, we can keep it as simple as gaining oxygen bonds.

So, if oxygen atoms are added to the molecule, that molecule has been oxidised.

Reduction can be thought of as losing bonds to oxygen

Reduction is the reverse of oxidation.

So, if oxygen atoms are removed from the molecule, or if a double bond to oxygen becomes a single bond to oxygen, that molecule has been reduced.

There are 3 main types of organic molecules which undergo oxidation:



Reaction 1: Oxidation of Primary Alcohols

Alcohols can be oxidised. If we think about the fact that oxidation involves the addition of oxygen atoms, we can ask which functional group has more oxygen atoms than alcohols? Carboxylic acids!

However, not all alcohol molecules can be oxidised

Remember, the carboxyl group can only be found at the end of a carbon chain. Therefore, only alcohols with the hydroxyl group on the 1st carbon atom can be oxidised to carboxylic acids.

Thinking back to that time we told you to remember the difference between primary, secondary and tertiary alcohols gives us some language to use here.

If we think about these classifications, remember that that oxidation of primary alcohols produces a carboxylic acid, but tertiary alcohols cannot be oxidised. That’s because we can’t fit any more bonds around the carbon bonded to the hydroxyl (-OH) group in tertiary alcohols.

Last year we said that primary alcohols oxidise to carboxylic acids directly, but now that we know a few more functional groups we can see that aldehydes are kind of halfway between an alcohol and a carboxylic acid.

Looking at the diagram below we see the alcohol has 1 bond to oxygen, the aldehyde has 2 bonds to oxygen (because of the double bond) and the carboxylic acids have 3.

H CC

H

H H

O

alcohol

1 bond to oxygen

CC C O H

aldehyde

Cr2O72-/H+ Cr2O7

2-/H+

2 bonds to oxygen

carboxylic acid

3 bond to oxygen

HO

CC

H

HH

O

First, the primary alcohol is oxidised to an aldehyde and then to the carboxylic acid.

In order to oxidise a primary alcohol, an oxidising agent must be added

Acidified dichromate solution (Cr2O72−/H+) is a good option, but acidified permanganate

(MnO4−/H+) also works.



These oxidation reaction are associated with colour changes

Acidified dichromate solution is orange. When it oxidises a primary alcohol dichromate is converted into chromium ions (Cr3+), which form a green solution. Permanganate on the other hand goes from a purple solution to form colourless Mn2+ ions when it has reacted.

Using ethanol as an example, the oxidation of primary alcohols looks like:

CH3-CH2-OH → CH3-CHO → CH3-COOH

We don’t have to start off with the primary alcohol, we can go straight from aldehydes to carboxylic acids through oxidation if we want.

Reaction 2: Oxidation of Secondary Alcohols

You may have noticed we said that “oxidation of primary alcohols produces an aldehyde and then a carboxylic acid, but tertiary alcohols cannot be oxidised”.

But, what about secondary alcohols?

Primary alcohols have their hydroxyl (-OH) group on the end of the molecule. When they undergo oxidation a carbonyl group (C=O) forms at the end. As we’ve seen, molecules with carbonyl groups on the 1st carbon are aldehydes.

Secondary alcohols have their hydroxyl (-OH) group somewhere else on the main chain that’s not the end carbon. If they are oxidised, the carbonyl group will end up in this position on the main carbon chain. As we’ve seen, molecules with carbonyl groups that aren't on the 1st carbon on the main chain are called ketones.

Secondary alcohols are oxidised to ketones

In order to oxidise a secondary alcohol, an oxidising agent must be added

In this case we’ll just use acidified permanganate solution (H+/MnO4−).

Using propan-2-ol as an example, the oxidation of secondary alcohols looks like:

CH3-CH(OH)-CH3 → CH3-CO-CH3

H+/Cr2O72− H+/Cr2O7

2−

H+/MnO4−



Reaction 3: Reduction of Aldehydes and Ketones

We can take the aldehyde and the ketone produced and go backwards to produce the primary or secondary alcohol, respectively.

In both cases a reducing agent, NaBH4 is used

It’s important to note that while we can reduce an aldehyde back to a primary alcohol, we can’t reduce carboxylic acids. NCEA likes to test students on this, so don't forget about NaBH4 as it is an important reducing agent!

Reaction 4: Oxidation of Alkenes

Alkenes can also undergo oxidation to form diols

Remember, diols are molecules with two hydroxyl (-OH) groups.

Again, an oxidising agent needs to be used

Just like with primary alcohols, acidified permanganate solution (MnO4−/H+) can be

added. However, acidified dichromate (Cr2O72−/H+) cannot be used.

Using ethene as an example, the oxidation of alkenes looks like:

CH2=CH2 → CH2(OH)-CH2(OH)

As this reaction proceeds, we will observe the purple solution of acidified permanganate turn colourless as manganese ions (Mn2+) are produced.

This may look a lot like an addition reaction, because we are breaking a carbon-carbon double bond and putting something on either carbon, but this is technically an oxidation reaction.

STOP AND CHECK:


What happens in an oxidation reaction. The types of organic compounds can undergo oxidation reactions. The two oxidising agents you need to know in Level 3 Chemistry.


H+/MnO4−



Substitution Reactions

In substitution reactions, there’s a tag team going on. Atoms leave the molecule and they get a mate to jump in and take their place.

e.g. CH3-CH2-Cl + KOH(aq)

the Cl atom is removed ... and is replaced by an OH group

CH3-CH2-Cl + KOH

heatCH3-CH2-OH + KCl

CH3-CH2- + K - OH

CH3-CH2-OH + K-Cl

Cl

When looking at substitution reactions it is important to ask yourself what is being taken away and what is being put in its place.

Since C-C and C-H bonds do pretty much nothing, we will always be swapping the interesting looking bits: halogen atoms (F, Cl, I, Br), hydroxyl groups (-OH) and amine groups (-NH2).

After that we can look at the reagent (the thing we add to our organic molecule) and see what might be substituted into our molecule. These are often things like halogen atoms, hydroxyl groups or amine groups; for example, the -OH from the KOH reagent.

Reaction 1: Haloalkane to Alcohol

To convert a haloalkane to an alcohol, the halogen atom needs to be removed and a hydroxyl group needs to be put in its place. The reagent that is added to the haloalkane is aqueous potassium hydroxide (KOH(aq)) and heat.

The KOH splits apart, the halogen comes off the carbon it is bonded to, the K and halogen combine to form potassium chloride or potassium bromide (depending on the halogen), and the OH group bonds to the same carbon atom.

Using chloroethane and bromoethane as the two examples, the overall reaction will look like either:

CH3-CH2-Cl + KOH(aq) → CH3-CH2-OH + KClCH3-CH2-Br + KOH(aq) → CH3-CH2-OH + KBr



Reaction 2: Haloalkane to Amine

Instead of adding aqueous potassium hydroxide to the haloalkane, we can add concentrated ammonia (NH3). What functional group contains a nitrogen atom? Amines! When concentrated ammonia is added to a haloalkane, the halogen comes off the carbon and combines with one of the hydrogens in ammonia to form a hydrogen halide (either hydrogen chloride or hydrogen bromide), and the leftover -NH2 bonds to the same carbon to form the amine.

You may have noticed that I keep calling the reagent “concentrated ammonia”. The fact that the ammonia is concentrated is super duper important! So, don’t forget to add that in.

Using chloroethane and bromoethane as the two examples, the overall reaction will look like either:

CH3-CH2-Cl + NH3(alc) → CH3-CH2-NH2 + HCl CH3-CH2-Br + NH3(alc) → CH3-CH2-NH2 + HBr

Reaction 3: Alcohol to Haloalkane

We’ve already seen alcohols being formed from haloalkanes with aqueous KOH. Going backwards requires the removal of the hydroxyl (-OH) group and the substitution of a halogen. In Level 3 Chemistry we are only interested in producing a chloroalkane, rather than a bromoalkane.

There are actually a handful of possible reagents that could be used - PCl3, PCl5 or SOCl2

Using ethanol as an example, the overall reaction with each of the possible reagents looks likes:

CH3-CH2-OH + SOCl2 → CH3-CH2-Cl (+ SO2 + HCl)3CH3-CH2-OH + PCl3 → 3CH3-CH2-Cl (+ H3PO3)CH3-CH2-OH + PCl5 → CH3-CH2-Cl (+ HCl + POCl3)

Reaction 4: Carboxylic Acid to Acyl Chloride

To convert a carboxylic acid to an acyl chloride let’s think what needs to change. Both have the carbonyl group, but connected to the carbonyl carbon in carboxylic acids is a hydroxyl (-OH) group and in an acyl chloride it is a halogen (a chlorine atom).

Therefore, we need to swap a hydroxyl group for a chlorine atom



We saw this in the alcohol to haloalkane reaction. This is the same, except both our reactant and product have that carbonyl group.

So you would expect similar reagents to be used and you would be right! However, an annoying detail is that PCl3 doesn’t work for this one, only PCl5 or SOCl2 can be used.

So, what actually happens in the reaction?

The hydroxyl group (-OH) of the carboxylic acid is removed.

When using SOCl2, one of the chlorines jumps on and bonds to the carbonyl carbon. The other chlorine from SOCl2 combines with the hydrogen from the hydroxyl group to form HCl. This leaves SO2 as the other by-product when it combines with the oxygen from the hydroxyl group. When using PCl5, one of the chlorines from it jumps on and bonds to the carbonyl carbon. Another chlorine from PCl5 combines with the hydrogen from the hydroxyl group to form HCl. The oxygen from the carboxyl group combines with the remaining reagent to form POCl3.

Using ethanoic acid as an example, the overall reaction will look like:

CH3-COOH + SOCl2 → CH3-COCl + SO2 + HCl Or

CH3-COOH + PCl5 → CH3COCl + POCl3 + HCl

Reaction 5: Acyl Chloride to Carboxylic Acid

We’ve seen how to get an acyl chloride from a carboxylic acid, but we can also go backwards and get our carboxylic acid back again.

This time we need to swap out the chlorine atom and get the hydroxyl group back. While, aqueous potassium hydroxide (KOH(aq)) was used to go from a haloalkane to an alcohol, we can’t use the same reagent in this case.

Just add H2O

Acyl chlorides react very vigorously with water – remember this fact as it will come back up later on! Adding H2O causes the chlorine to come off the acyl chloride. The carbonyl carbon then binds to the -OH from water, forming the carboxylic acid.

The remaining hydrogen from water and the chlorine that was removed then combine to form HCl as a by-product.But this is not just any old HCl, this is HCl in the gaseous state.



Using ethanoyl chloride as an example, the overall reaction will look like:

CH3-COCl + H2O → CH3-COOH + HCl(g)

Reaction 6: Acyl Chloride to Amide

To convert an acyl chloride to an amide let’s think what needs to change. Both have the carbonyl group, but connected to the carbonyl carbon in acyl chlorides is a halogen atom (a chlorine atom) and in amides it is an amine (-NH2) group.

Therefore, we need to swap a chlorine atom for an amine group

We saw this in the haloalkane to amine reaction. This is the same, except both our molecules have that carbonyl group.

However, the same reagent is used: concentrated ammonia (NH3).

So, what actually happens in the reaction?

The chlorine atom from the acyl chloride is removed. The -NH2 from ammonia then jumps on to form our amide. The remaining hydrogen from ammonia combines with chlorine to form hydrogen chloride (HCl).

Using ethanoyl chloride as an example, the overall reaction will look like:

CH3-COCl + NH3(alc) → CH3-CONH2 + HCl(g)

STOP AND CHECK:


The definition for a substitution reaction. The possible kinds of functional groups that may be swapped in a

substitution reaction.


Neutralisation Reactions with Carboxylic Acids

Time for a throwback to Level 1 Science. Think back to the Acids and Bases external.

Remember that, a reaction between an acid and a base is known as a neutralisation reaction. It is called this, because when an acid reacts with a base, the products we end up with are neither acidic nor basic: they are neutral!



In general, all neutralisation reactions follow this simple format:

Acid + base salt + waterA salt is simply some neutral ionic compound.

When writing a reaction, we can begin by filling in the left hand side, which is where the acid and base go, as well as part of the right hand side, where we know water will always end up. We then use the parts of the acids and bases that don’t react into water to make up our salt.

But hold up.

Just like any other acid, Carboxylic acids can be involved in neutralisation reactions. Here are some examples:

1. Carboxylic acid + water: CH3COOH(aq) + H2O(l) ⇌ CH3COO-(aq) + H3O+(aq)

2. Carboxylic acid + metal carbonate: 2CH3COOH(aq) + Na2CO3(aq) → 2(CH3COO-) 2Na+

(aq) + H2O(l) + CO2(g)

3. Carboxylic acid + base: CH3COOH(aq) + NH3(aq) → CH3COO−(aq) + NH4

+(aq)

The key to remember here, is that every time the Carboxylic acid reacts, it loses a Hydrogen to form an ion or salt on the product side.

water

donates proton

propanoic acid

+

-+

CH3 CH2 CO O

H HO H

OH

H

Hpropanoate acid hydronium ion

+CH3 CH2 CO

O

STOP AND CHECK:

Turn your book over and see if you can remember the main carboxylic acid reactions using a different carboxylic acid molecule as an example.



Acid-Base Reactions involving Amines

There are 2 main acid-base reactions involving amines, which are similar to some of the carboxylic acid reactions:

Amine + water: CH3CH2NH2(aq) + H2O(l) ⇌ CH3CH2NH3+(aq) + OH−

(aq)

Amine + acid: CH3CH2NH2(aq) + HCl(aq) → CH3CH2NH3+(aq) + Cl−(aq)

When a base reacts with water, water acts as an acid to complement it. Here, water donates a proton to the amine, leaving hydroxide (OH−) ions in solution. As the the hydrogen ion (proton) joins onto the amine group, we say the amine is protonated.In reactions with acids, the amine gains a hydrogen ion (proton) from the acid, leaving a protonated amine and a spare ion from the acid.

wateramine accepts proton

hydroxide

propanamine

+

-+

CH3 CH2 CH2

H OH HH

N

+CH3 CH2 CH2

H

HN O HH

Again, it’s important to remember that, unlike amines:

Amides are not bases

You don’t need to know the exact reason, but basically the oxygen atom stops the nitrogen from acting as a base and accepting protons.

You may have noticed earlier on when we were doing substitution reactions that we didn’t walk through converting carboxylic acids to amides.

That’s because we can’t convert carboxylic acids to amides directly

If we were to add some ammonia to our carboxylic acid to try and get that OH substituted for an NH2, we wouldn’t get a substitution reaction at all but instead we would get an acid base reaction!

In order to make an amide from a carboxylic acid we would first have to turn our carboxylic acid into an acyl chloride and then turn our acyl chloride into an amide.



STOP AND CHECK:


The 2 main amine reactions using a different amine molecule as an example. Why we cannot react a carboxylic acid and ammonia together to get an amide.

Condensation Reactions

It’s tempting to think that condensation reactions in organic chemistry involve water vapour changing state into liquid water. Now that would be too easy!

A condensation reaction involves joining two smaller molecules together to create one larger molecule.

When these two molecules are joined together, a smaller molecule, such as water, is squeezed out and removed.

two moleculesjoin together...

...and get rid of a smaller one

CH3 +C CH3 + H2OO HO

OHCH3 C

CH3

O

O

Reaction 1: Carboxylic Acid + Alcohol to Ester

An ester has two components:

1. A carboxylic acid2. An alcohol

Imagine taking a carboxylic acid and removing the hydroxyl part (-OH) of the carboxyl (-COOH) group at the end of the molecule. The carbonyl carbon needs to bond to something else.

Now, take an alcohol molecule and remove the hydrogen from hydroxyl (-OH) group. The oxygen it was bonded to now needs to bond to something else.

Time to join the two:

The carboxylic acid and alcohol are joined where the hydrogen was removed from the carboxylic acid, and where the hydroxyl group was removed from the alcohol.



We took a hydrogen away from the carboxylic acid and a hydroxyl (-OH) away from the alcohol. These two will combine to form water (H2O).

So, why is this a condensation reaction?

Producing an ester from a carboxylic acid and an alcohol is an example of a condensation reaction because we are taking two large molecules and essentially just joining them together. But in the process we are removing a small molecule, which is water in this case.

You may be thinking that this reactions looks a bit like a substitution reaction, and you would be correct. We’re swapping the hydroxyl group from the carboxylic acid with an alcohol molecule to form an ester - i.e. groups of atoms are being removed and new atoms are being added on. In this way, condensation reactions are just a special type of substitution reaction.

But wait! We need a few extra reagents

Since we are removing water, it’s a good guess to think we need a dehydrating agent for the reaction to go ahead. That’s absolutely true, and acid (H+) is used as a dehydrating agent.

Heat is also needed for this reaction to go ahead.

Using ethanol and ethanoic acid as an example, the overall reaction will look like:

CH3-COOH + CH3-CH2-OH → CH3-CO-O-CH2-CH3 + H2O

The reaction above is also called esterification as we are making an ester.

Reaction 2: Acyl Chloride + Alcohol to Ester

We’ve already seen how we can produce an ester from combining a carboxylic acid and an alcohol. A similar reaction can be done with an acyl chloride rather than a carboxylic acid.

This time we simply remove the Cl from the acyl chloride and the hydrogen from the hydroxyl group of the alcohol.

Time to combine the two:

The acyl chloride, with the Cl removed, is attached to the oxygen atom chilling on the alcohol molecule.

We took a Cl from the acyl chloride and a hydrogen from the hydroxyl group of the alcohol. These combine to produce hydrogen chloride.

H+ + heat



This time we don’t need additional reagents. This is because acyl chlorides are much more reactive on their own compared to carboxylic acid + alcohol esterification.


Producing an ester from an acyl chloride and an alcohol is an example of a condensation reaction because we are taking two large molecules and essentially just joining them together. But in the process we are removing a small molecule, which is hydrogen chloride (HCl) in this case.

Using ethanol and ethanoyl chloride as an example, the overall reaction will look like:

CH3-COCl + CH3-CH2-OH → CH3-CO-O-CH2-CH3 + HCl

Reaction 3: Acyl Chloride + Amine to Amide

Rather than adding an alcohol to an acyl chloride to produce an ester we can add an amine instead to produce a kind of amide.

We simply remove the Cl from the acyl chloride and a single hydrogen from the amine group of the amine.

Time to combine the two:

The acyl chloride with the Cl removed is attached to the nitrogen atom chilling on the amine molecule.

We took a Cl from the acyl chloride and a hydrogen from the amine group of the alcohol, and these combine to produce hydrogen chloride.

We don’t need additional reagents.


Producing an amide from an acyl chloride and an amine is an example of a condensation reaction because we are taking two large molecules and essentially just joining them together. But in the process we are removing a small molecule, which is hydrogen chloride (HCl) in this case.

Using ethanamine and ethanoyl chloride as an example, the overall reaction will look like:

CH3-COCl + CH3-CH2-NH2 → CH3-CO-NH-CH2-CH3 + HCl



Although it doesn’t look like our typical amide since it has an extra carbon chain hanging off the nitrogen, because we have the carbonyl group bonded to a nitrogen it’s still an amide. It doesn’t matter that one of the hydrogens on the nitrogen has been replaced with a carbon chain.

STOP AND CHECK:


The requirements for a reaction to be classified as a “condensation reaction”. The 3 examples of condensation reactions you need to know.


Hydrolysis

Hydrolysis is a reaction where large molecules, such as polymers, triglycerides or polypeptides (which we’ll cover later), are broken down into smaller molecules. We can also hydrolyse esters.

You can either destroy these large molecules by just adding water

Hydrolysis is simply the breakdown of a compound due to the reaction with water. We can make it acidic or basic as well.

With acid hydrolysis, any functional groups that can be protonated (have a proton added), such as amine or carboxyl groups, will be protonated.

But with base hydrolysis any functional groups that can be de-protonated (have a proton removed), such as amine or carboxyl groups again, will be de-protonated.

The hydrolysis of esters will be illustrated using triglycerides in the next section

STOP AND CHECK:


The role of water in hydrolysis reactions. The difference between acid and base hydrolysis in general terms. What kinds of molecules can be hydrolysed.




Triglycerides and their Hydrolysis

Wibbly-wobbly body fat in humans and other animals is mostly composed of triglycerides, which is derived from two things called glycerol and fatty acids. These triglycerides are just 3 ester groups in the same molecule.

Glycerol, which is also called “propan-1,2,3-triol”, is a triol (an alcohol with 3 -OH groups) which makes up the backbone of the triglyceride.

Free fatty acids, which are just carboxylic acid molecules with long hydrocarbon chains, are joined to this glycerol backbone through an esterification reaction to produce the triglycerides.

Really, this is simply an alcohol + carboxylic acid → ester reaction but with more complicated examples

saturated triglyceide

n = any positive whole number. Used because the length of the chains can vary

CH2 O CO

CH3(CH2)n

CH O CO

CH3(CH2)n

CH2 O CO

CH3(CH2)n

When there are no double or triple bonds in the free fatty acids, the fats will be saturated, just like regular hydrocarbon chains.When there are double or triple bonds in the free fatty acids, the fats will be unsaturated - again, just like regular hydrocarbon chains.

Let’s have a look at the hydrolysis of triglycerides:

Triglycerides are made from a glycerol backbone and 3 fatty acids.

We can use acid or base hydrolysis with triglycerides:

Let's take a look at acid hydrolysis first:

H2C

H2O/H+

+

O C

O

CH3(CH2)16

H2C O C

O

CH3(CH2)16

H2C O C

O

CH3(CH2)16 3 x CH3 C

O

OH(CH2)16

CH2

OH OH OH

CH2 CH2



The -OH from water joins onto the glycerol backbone to form the triol. With acid hydrolysis “any functional groups that can be protonated will be protonated”. As there are H+ ions present due to the acid, a carboxylic acid is formed from each fatty acid.

And base hydrolysis:

H2C

+

O CO

CH3(CH2)16

H2C O CO

CH3(CH2)16

H2C O CO

CH3(CH2)16 3 x CH3 CO

O–(CH2)16

CH2

OH OH OH

CH2 CH2

Just like with acid hydrolysis, the -OH joins onto the glycerol backbone to form the triol.With base hydrolysis there are no H+ ions available, and so “any functional groups that can be de-protonated will be de-protonated”. Rather than forming a carboxylic acid the carboxylate ion with the negatively charged -COO− group is formed. If we use a base such as NaOH, the Na+ will combine with the carboxylate ion to form a carboxylate salt: Na+ + CH3-(CH2)16-COO− → CH3-(CH2)16-COONa.

STOP AND CHECK:


The two components of triglycerides. The name of the reaction that produces triglycerides. The difference between saturated and unsaturated triglycerides. How triglycerides can be hydrolysed - what’s the difference between acid and

base hydrolysis of triglycerides (and esters in general)?


Distillation, Reflux and Separating Funnels

All of the reactions we have discussed can be performed in the classroom. However, they require a few experimental techniques, particularly distillation and reflux.

Distillation is used to purify products

When reactions go ahead and products are made, sometimes the product is



contaminated with impurities or there are additional unwanted products. Impurities or unwanted products are removed by separating them from the main product.

For example, distillation can be used to separate ethanol from water.

Distillation separates compounds based on their boiling point. That’s because different compounds have different boiling points, so the impurities will have a different boiling point from the main product.

Distillation occurs in an apparatus that looks like:

Thermometer

Round-bottom flask

Fractionatingcolumn

Bunsen burner

Water

Water

Condenser

Let’s separate ethanol from water as our example.

The mixture of ethanol and water is heated in a round-bottom flask. Since ethanol has a lower boiling point than water (78°C versus 100°C) it will evaporate (being converted from a liquid to a gas) first.

The ethanol gas rises up the fractionating column and travels down the condenser while the water is left behind in the flask. The condenser is quite cold and so any gas that hits it will condense back into the liquid state. The liquid - which only contains the evaporated product (ethanol in this case) runs down the condenser tube and is collected into another flask. The unwanted stuff left in the round-bottom flask can now be chucked away.

Another important use of distillation is in the production of aldehydes. We have already mentioned that oxidation of primary alcohols takes place in two steps, the first where the alcohol goes to an aldehyde and the second takes the aldehyde to the carboxylic acid.

How can we stop the reaction at the aldehyde? The answer is distillation. Aldehydes have a much lower boiling point than either alcohols or carboxylic acids due to their



lack of hydrogen bonding (you do not need to know that for the organics standard, but if you have done thermochemistry this will be familiar to you).

First we put some primary alcohol, let's say propan-1-ol, in our round bottom flask and heat it up then add some oxidising agent, such as permanganate. When the propan-1-ol is oxidised to propanal, the propanal will boil and turn into gas.

When the propanal boils, it will rise up the tube and hit the condenser, condense back to a liquid and run down the side tube to be collected. The important point here is that once it has been boiled and removed, it cannot be oxidised any more because the permanganate is still stuck down in the solution.

We have taken out the aldehyde from our solution as soon as it is formed which prevents it from being oxidised again to make the carboxylic acid.

Many reactions are “heated under reflux” - but what does this mean?

Some organic reactions are far too slow and require heat to increase the rate of reaction. The problem is that many organic compounds have relatively low boiling points and so heating the mixture will cause them to evaporate. They escape and either the reaction doesn’t have enough reactants or the products are lost.

Heating under reflux uses a condenser to stop the reagents from escaping.

Heating under reflux requires an apparatus that looks like:

Heat

WaterReactants

Water in

Water Out

When the organic compounds are evaporated, they rise in the condenser column. The function of the condenser is to convert the gas back into a liquid by pumping water around the outside of the column to cool it down. In distillation, the condensed liquid flowed away down that side tube but in reflux there is no side tube and so the liquid



has no choice but to fall back down into the flask and keep reacting, which is what we want.

Heating under reflux allows reactions, such as triglyceride hydrolysis to occur.

In summary, reflux involves heating an organic reaction over and over again to increase the reaction rate without losing any reactants or products.

Let’s quickly touch upon separating funnels

Separating funnels look like:

High Density Liquid

Low Density Liquid

Tap

Sometimes an organic reaction will produce two separate layers which are separated based on density - they don’t mix because one might be polar and the other non-polar (like a mixture of oil and water) or they might be different densities (like water and honey) or both.

Separating funnels allow us to separate two different liquids that have different properties. If distillation was separating compounds based on them having different boiling points, separating funnels are used to separate liquids based on a difference in polarity or density (or both). As the tap is opened, the bottom layer can be run off and be separated from the other layer.

STOP AND CHECK:


The purpose and process of distillation. The purpose and process of reflux. The purpose and process of separating funnels.

Try explain it in your own words.



POLYMERS, AMINO ACIDS AND PROTEINSThis section includes a few concepts that were covered in level 2 organic chemistry but we are going to revisit them here so no need to worry.

We are also going to talk about amino acids and proteins, which are very interesting classes of molecules that are really important in biology.

To keep it nice and simple, all you need to know is:

What a condensation polymer is and how they can be formedHow to identify an amino acid and how to combine them together

Polymers

A polymer can be described as a very large molecule composed of repeating units

These repeating units are smaller molecules called monomers, which must be joined together to form this continuous polymer.

Last year you may remember that alkenes can undergo a special kind of addition reaction - a polymerisation reaction - where they are joined together to form a polymer. These addition polymers are not assessed in Level 3.

But what is assessed is the condensation polymers:

Polymers can also be formed by condensation polymerisation reactions

There are two main types of polymers formed by condensation reactions:

Polyesters are made by joining carboxylic acid or acyl chloride groups and alcohol groups to form an ester linkage.

Polyesters can be made by combining two different monomers, where one is a dicarboxylic acid (carboxylic acids with a carboxyl group on either end of the molecule) or diacyl chloride (acyl chlorides with an acyl chloride group on either end of the molecule), and the other is a diol. Polyesters can also be made from a single monomer which has a carboxylic acid (or acyl chloride) at one end and a hydroxyl group at the other end.



Polyamides are made by joining amine groups and acyl chloride groups to form an amide linkage. Again, this can be made by two different monomers - a diamine (amine group on either end) and a di-acyl chloride - or from a single monomer with an amine and acyl chloride group on opposite ends.

In each case, a smaller inorganic molecule, such as H2O or HCl, is removed. This is just like in condensation reactions, which is why these reactions form condensation polymers!

Forming polyesters:

The idea is that we’ll first remove a hydroxyl (-OH) group that is part of the carboxyl (-COOH) groups in the di-carboxylic acid, and then remove the hydrogen from the hydroxyl group (-OH) of the diol.

The carbonyl carbon needs to bond to something else and so does the oxygen attached to the alcohol in order to satisfy their valence shells. So, the carbonyl carbon bonds to oxygen and so joins the carboxylic acid and alcohol to form the polyester.

The important thing to realise is that each of these monomers can form two ester linkages at either end of the molecule because they have a functional group at both ends. That way, a whole bunch of molecules can link together and essentially go on until we run out of monomers in our solution.

If there was only one functional group per molecule then we couldn’t form a polymer.

Polyester

1,3 propandioic acid

carboxylic acidpart

carboxylic acidpart

alcoholpart

alcoholpart

imagine lining them up alternately:

3 ester linkages shown

esters are made with each acid group and each alcohol group

diol (methan -1, 2 - diol)

HO C CH2

O

OHC

O

HO. . .

. . . . . .

. . .C CH2

O

OHC

O

C CH2

O

C

O

C CH2

O

C

O

HO+ CH2 OH

H O CH2 O H

O CH2 O O CH2 O

H O CH2 O HHO C CH2

O

OHC

O

The hydrogen atoms and hydroxyl groups combine to form water that is a by-product.



Remember, we can also form polyesters from a single monomer with both functional groups on either end. The important thing is just that both functional groups are involved.

Let’s have a look at an example with 4-hydroxybutanoic acid - a molecule with a carboxyl and an hydroxyl group:

4- hydroxybutanoic acid

imagine lining up lots and lots of monomers

esters are made with each acid group and each alcohol group

HO CH2CH2 OHCO

CH2

HO CH2CH2 OHC

O

CH2

O CH2CH2 OC

O

CH2 CH2CH2 C

O

CH2 O CH2CH2 C

O

CH2

HO CH2CH2 OHC

O

CH2 HO CH2CH2 OHC

O

CH2

Polyester

. . . . . .

1st 4 - hydroxybutanoic acid monomer

2nd monomer 3rd monomer

Forming a polyamide:

This time, we remove the chlorine (-Cl) from each acyl chloride (-COCl) group on the di-acyl chloride acid and then just one hydrogen atom from each amine (-NH2) group on the di-amine.

The carbonyl carbon then joins to the nitrogen on neighbouring di-amine molecules.

imagine lining them up alternately:

amides are made with each acyl chloride group and each amine

H2N NH2(CH2)6 (CH2)8

N N(CH2)6

Cl+O

C Cl

O

C

(CH2)8Cl

O

C Cl

O

C

(CH2)8

O

C

O

C (CH2)8

O

C

O

C

(CH2)8Cl

O

C Cl

O

C

Polyamide

. . .. . .

amine part acyl chloride part amine part acyl chloride part

a diamine (1, 6 - diaminohexane) a di - acyl chloride (decanedioyl chloride)

H

H

H

H

N N(CH2)6. . . . . .

H

H

N N(CH2)6

HH

N N(CH2)6

H

H

H

H



Again, we can have a single monomer with both functional groups on either end. The important thing in polyamide formation is that there we involve both an acyl chloride and an amine.

STOP AND CHECK:


How polymers can be formed by condensation reactions.


Amino Acids and Proteins

Polymers are all around us, including inside the human body. For example, DNA is a polymer of nucleic acids, while proteins, or polypeptides, are polymers of amino acids.

In Level 3 Chemistry, you need to be able to identify (but not name) an amino acid and explain how they are joined together to form a protein (polypeptide)

All amino acids contain an amine (-NH2) group and a carboxyl (-COOH) group attached to a central carbon, as well as a specific side chain which is unique to each and every amino acid.

e.g.

carboxyl group

H2N C

H

COOH

R

H2N C

H

COOH

CH3

specific side chain

amino group

Amino acids can be joined together by the peptide bond, which forms between the amino nitrogen and the carboxyl carbon, after a hydrogen (H) from the amine and a hydroxyl group (-OH) from the carboxyl are removed.

This peptide bond is simply just an amide linkage, or amide bond, as we have a carbonyl group with a nitrogen bonded to the same carbon.



peptide bond(also called an amide bond)

H2N C

H

COOH +CH3

H2N C

H

COOHN

H

CH3

C

CH3

C

O

H2N C

H

COOHCH3

H

The first example showed a peptide bond forming between two identical amino acids. But, we can also join two different amino acids:

peptide bond(also called an amide bond)

H2N C

H

COOH +H

H2N C

H

COOHN

H

H

C

CH3

C

O

H2N C

H

COOHCH3

H

STOP AND CHECK:


The general structure of an amino acid. How amino acids are joined together. The name of the bond connecting monomers in proteins.


Quick Questions

What are polymers and how are they formed? What are polypeptides and how are they formed?

?



PROPERTIES OF ORGANIC COMPOUNDSWaaaaay back at the start of the Walkthrough Guide, we said that functional groups are super duper important because they affect the chemical and physical properties of the compound. Now that you should be familiar with the main functional groups out there, we can now link structure with function.

First we’ll revisit the idea of polarity - covered in more depth in Structure and Bonding - and use this to classify our organic molecules as polar or non-polar. Next, we’ll think about what affects melting and boiling point, and use the structure of our organic molecules to explain which ones melt or boil at the highest temperatures. Finally, we’ll look at the idea of solubility and use the general rule “like dissolves in like” to explain which of our organic molecules will dissolve in water and which ones won’t.

Introduction to Polarity

Polarity is important in Organic Chemistry as it can tell us a lot about the properties of a molecule, from whether it will dissolve in water, to the temperature at which it boils. So, what is polarity?

Arctic (North Pole)

magnet

Antarctica (South Pole)

S

Npolarity

On opposite ends of the planet, Earth has a North and South pole. If have a look at magnets, we call one end the north pole and the other end the south pole. Because of this, both the Earth and magnets are said to be polar, or have polarity.

Chemical bonds and molecules can also be polar (or non-polar)

Here, polarity just means the “separation of charge”.



Polar molecules will have a positively-charged region and a negatively-charged region, while non-polar molecules will have no real charge difference across the molecule. In a polar covalent bond, one of the atoms ends up with a partial positive charge while the other a partial negative charge. In a non-polar covalent bond, there is no difference in charge.

To help us understand whether molecules are polar or non-polar we need to talk about something called, “electronegativity”.

All atoms are attracted to bonding electrons, but some are more attracted to them than others

The stronger their feelings for these electrons, the stronger the attraction, and the tighter the atom will hold onto electrons in a covalent bond. This is the electronegativity.

It can be defined as, “the tendency of an atom to attract bonding electrons”.

So, how do you know which atoms are more attracted to bonding electrons than others?

If you go down a group in the Periodic Table the electronegativity decreases, but if you go across a period (from left to right), the electronegativity increases.

Na0.9

Ag2.1

Cu1.9

Cd1.7

Zn1.6

Co1.9

Ni1.9

Fe1.8

Electronegativity increases across period

Ir2.2

Pt2.2

Cs0.7

Ba0.9

Rb0.8

K0.8

Li1.0

H2.1

Rh2.2

Pd2.2

Tl1.8

In1.7

Ga1.6

Al1.5

B2.0

Hg1.9

C2.5

N3.0

O3.5

F4.0

Au2.4

Sr1.0

Ca1.0

Mg1.2

Be1.5

La1.0

Y1.2

Sc1.3

Hf1.3

Zr1.4

Ti1.5

Ta1.5

Nb1.6

V1.6

Cr1.6

Mn1.5

W1.7

Re1.9

Tc1.9

Mo1.8

Pb1.9

Sn1.8

Ge1.8

Si1.8

Bi1.9

Sb1.9

As2.0

P2.1

Po2.0

Te2.1

Se2.4

S2.5

At2.1

H2.5

H2.8

Cl3.0

Rn

Xe

Kr

Ar

Ne

He

Elec

trone

gativ

ity d

ecre

ases

do

wn

a gr

oup

Os2.2

Ru2.2

This means that the least electronegative atoms are cesium and francium, whereas the most electronegative atoms are nitrogen, oxygen and fluorine. (We ignore the Noble Gases since they are unreactive).



Let’s grab two identical non-metal atoms, say two hydrogen atoms

They both have 1 valence electron but need 2 in total to be stable. Sharing them sounds like a great idea at this point!

Even though they want to share, both hydrogen atoms secretly want the electrons to themselves. So, there is a bit of tug of war going on. But, because both atoms are the same they pull on these bonding electrons with the same amount of strength. This means that bonding electrons will happily zip around the nucleus of both hydrogen atoms, spending the same amount of time around each one.

This means there is no real difference in charge between these two atoms, so their covalent bond is non-polar.

symmetrical electron distribution

H H

e

e

What happens when we get two different non-metal atoms, say a hydrogen atom and a chlorine atom?

Chlorine has 7 valence electrons but needs 8, while hydrogen has 1 but needs 2. So, they both decide to share 1 electron.

Since chlorine is more electronegative than hydrogen, chlorine has a larger tendency to attract the bonding electrons; bonding electrons are attracted more to the chlorine than they are to the hydrogen. Although the 2 bonding electrons are shared, chlorine pulls more tightly on them. We end up with the bonding electrons spending more time around chlorine nucleus than with hydrogen.

Partial charges

Since chlorine isn’t being fair and is being greedy instead (and because electrons are negatively charged), it ends up with a partial negative charge, which is represented by the “delta negative” symbol (δ-).

To give hydrogen something to be happy about, it ends up with a partial positive charge, which is represented by the “delta positive” symbol (δ+).



This kind of covalent bond is polar

That’s because there is a separation of electrical charge. Since it is polar it creates what is called a, “dipole”, which is the separation of electrical charge that we just talked about.

uneven electrondistribution

partial negativechargepartial positive

chargeH Cl

e

eδ+ δ+

As a general rule in Organic Chemistry:

If there are no highly electronegative atoms, like oxygen or nitrogen atoms, attached to the main carbon chain the molecule will likely be non-polar. If there are oxygen or nitrogen atoms in the functional group then the molecule is likely to be polar.

STOP AND CHECK:


The definition of polarity when it comes to chemistry. How polarity can be applied to molecules and covalent bonds. What electronegativity is. Which atoms have higher electronegativity values, and which ones

have lower values. What are the requirements to make a non-polar covalent bond in terms

of the atoms – are they the same or different atoms? Why non-polar covalent bonds have no separation of charge. What are the requirements to make a polar covalent bond in terms

of the atoms – are they the same or different atoms? Why polar covalent bonds have no separation of charge.


Polarity of Organic Compounds

If we consider the organic compounds containing just carbon and hydrogen atoms - alkanes, alkenes and alkynes - we can say that they are always non-polar no matter how long the carbon chain is.



Alkane, alkene and alkyne molecules have a symmetrical shape which makes them non-polar molecules.

Generally speaking, haloalkanes are also considered non-polar…

If you’ve had a look at Structure and Bonding already, you hopefully remember that halogens are quite electronegative – more so than carbon and hydrogen. This would lead anyone to believe that haloalkanes are polar due to this negatively-charged region.

The halogen can scream negative all it likes, but the non-polar carbon chain drowns out the noise from the halogen, making the molecule non-polar overall - it doesn’t take much to be drowned out. The addition of a halogen atom was a nice touch, but it’s not drastic enough to make haloalkanes that much more exciting than alkanes in terms of polarity.

Small haloalkanes with fluorine will be polar as fluorine is the most electronegative element. But overall we consider haloalkanes to be non-polar.

This means they essentially just have the same properties as alkanes, alkenes and alkynes.

Compounds containing oxygen or nitrogen atoms are usually polar overall

Oxygen and nitrogen are very electronegative atoms - more so than carbon and hydrogen atoms. This means when you’ve got one of these atoms attached to the main carbon chain there is a region of negative charge, giving the molecule polarity.

Alcohols, amines and all compounds with a carbonyl group contain these atoms. Alcohols have the hydroxyl group (OH−) composed of an oxygen atom bonded to a hydrogen and amines have the amine group composed of a nitrogen atom bonded to two hydrogen atoms (NH2). Carboxylic acids, esters, amides, acyl chlorides, ketones and aldehydes all contain the carbonyl group (C=O), composed of a carbon atom double bonded to an oxygen atom.

Carboxylic acids also contain a hydroxyl group (-OH), adding additional polarity.

ethanol

hydroxyl group

CH3 CH2 OH

ethanamine

amine group

CH3 CH2 NH2

ethananoic acid

carboxyl group

CH3 CO

OH



Therefore, it would be reasonable to think that all these molecules are polar molecules.

Only small alcohols, amines and compounds with carbonyl groups are polar

When these organic molecules are small - generally less than 5 carbon atoms - the polar functional group takes up a large enough proportion to make the molecule polar overall.

As more carbon atoms are added to the main carbon chain the polar functional groups take up a smaller and smaller proportion of the molecule. They are essentially silenced by the large non-polar carbon chain. This means that large molecules - with more than 5 carbon atoms - are generally considered to be non-polar.

ethanol octanol

= polar

CH3 CH2 OH

= essentially non-polar

CH3 CH2 CH2 CH2 CH2 CH2 CH2 OH

In an exam situation you will either be given a really short chain or a really long chain, and so the distinction of whether they are going to be polar or non-polar will be much easier.

STOP AND CHECK:


Why alkanes, alkenes and alkynes are non-polar. Whether haloalkanes are polar or non-polar. Which organic molecules are considered polar - are they always polar?


Introduction to Melting/Boiling Point

All substances can exist as gases, liquids and solids at different temperatures and pressures

For example, water molecules exist as a solid (ice) at temperatures below 0°C. As we turn up the dial and get things heated up, the ice melts and forms liquid water. If we want to take things to the next level, we can boil the water up to 100°C and produce a gaseous form of water (steam).



When the temperature increases the amount of heat energy in the system increases

This is used to break any bonds holding the solid or liquid together.

As a general rule, the stronger the force of attraction the more heat energy is required to break it. (We will get onto which forces are stronger than others in the next few sections but keep this in mind as we go through because it is really important).

The melting point is the temperature at which solid melts into a liquid, while the boiling point tells us what temperature is needed to boil that liquid into a gas.

solid

intermolecular force

melting

liquid

gas

boiling

There are 3 intermolecular forces

These are:

1. Instantaneous dipole-dipole forces between all molecules. 2. Permanent dipole-dipole forces between polar molecules only. 3. Hydrogen bonding between molecules containing a hydrogen bonded to a highly

electronegative atom – only worry about oxygen and nitrogen in Level 3 Organic Chemistry.

These different intermolecular forces have different strengths

Instantaneous dipole forces are the weakest, followed by permanent dipole forces, with hydrogen bonding being the strongest. If you need some more information jump over to the Level 3 Thermochemistry cram guide. This won’t be directly assessed in this standard, but it will help you out a lot if you understand these trends.



STOP AND CHECK:


How solids are converted to liquids and how liquids are converted to gases. The 3 intermolecular forces and their relative strengths.


Melting/Boiling Point of Organic Compounds

Alkanes, alkenes, alkynes and haloalkanes have lower melting and boiling points

All of these molecules are non-polar and are held together by instantaneous dipole-dipole forces. As these are weak forces, it doesn’t take much energy in the form of heat to break them, transforming a solid into a liquid, or liquid to gas, easily. This is why alkanes, alkenes, alkynes and haloalkanes are often gases at room temperature.

Alcohols, amines and compounds with carbonyl groups have higher melting and boiling points

Compared to alkanes, alkenes, alkynes and haloalkanes, these organic compounds have higher melting and boiling points when the carbon chains are the same length.

Because alcohols, amines and compounds with carbonyl groups are polar molecules, they are held together by permanent dipole-dipole forces which are stronger than the instantaneous dipole-dipole forces between non-polar molecules. This is because there is a continuous attraction between the positively-charged and negatively-charged regions of neighbouring molecules.

This explains why all alcohols are either liquid or solids at room temperature, similar to amines and compounds with carbonyl groups.

Alcohols and carboxylic acids are also held together by hydrogen bonds which are the strongest intermolecular force, so will have the highest melting and boiling points.

For all organic molecules, the melting and boiling point increases as the carbon chain length increases

This is because the strength of intermolecular forces depends on the number of electrons, and as the molecular mass increases the number of electrons also increases. This leads



to stronger attractive forces between molecules, meaning more heat is required to break the bonds.

Carbon atoms in a straight chain have higher melting/boiling points than branched chains

When all the carbon atoms are in a straight chain these intermolecular forces can do their job more easily, leading to stronger attractive forces.

Essentially, the straighter the chain is, the closer the two molecules can get to one another. There is a much greater contact area and so a greater the amount of instantaneous dipole-dipole forces will exist.

Boiling point = 36° C Boiling point = 9.5° C

CH3

CH3 CH3

CH3

CH3 CH3

CH3

CH3

C

C

CH3CH3

CH2

CH2

CH2

CH3 CH3

CH2

CH2

CH2

STOP AND CHECK:


The name of the attractive force that holds molecules together. Why alcohols have higher melting/boiling points than alkanes, alkenes,

alkynes and haloalkanes of similar lengths. The trend in melting/boiling points of organic molecules when the carbon

chain increases. Whether straight or branched chains have higher melting/boiling points,

and the reasons why.


Introduction to Solubility

Solubility tells us how likely something is to dissolve in something else. If a compound is soluble in water it will dissolve when added.



The golden rule of solubility is that “like dissolves in like”

So, polar molecules dissolve in water, which is a polar liquid, but not in non-polar liquids.

On the other hand, non-polar molecules dissolve in other non-polar liquids but not in water. You will always be told if a solvent is non-polar. For example, it might say something like “hexane, a non-polar solvent…”

The thing that gets dissolved in the liquid is called the “solute”, while the liquid it dissolves in, such as water, is called the “solvent”.

molecule

water molecule

solid

intermolecular force

a solution

bonding with water

O

O

O

O

H

H

H

H

H

H

H

H

O

H

H

dissolving

STOP AND CHECK:


What solubility means, and the rules that determine if something is soluble in something else.


Solubility of Organic Compounds

The solubility of organic compounds comes back to the idea that “like dissolves in like”. In Level 2 Organic Chemistry we are interested in dissolving these organic compounds in water.

Do alkanes, alkenes, alkynes and haloalkanes dissolve in water? Nope!



That would be too much fun for them. The reason is that they are all non-polar molecules due to being symmetrical. Because we know that “like dissolves in like”, we know that these non-polar molecules are insoluble in polar liquids, like water.

Instead, they don’t mix, and instead form separate layers. If you wanted to show you off, you could say that alkanes/alkenes/alkynes/haloalkanes and water and immiscible.

tap

water

nomixing

alkane

Some alcohols, amines and compounds with carbonyl groups are soluble in water.

Pour a bit of alcohol, amine or carbonyl-containing compounds into some water and POOF! It’s gone. It dissolves in the water because “like dissolves like”, and polar molecules are soluble in polar liquids, like water. This only works for small molecules, like those with between 1 and 4 carbon atoms in their main chain.

As we stretched out the molecule to 5 or more carbon atoms they begin to resist. Rather than mixing and mingling with the water molecules, the alcohol, amine or carboxylic acid sulks in the corner and instead forms a separate layer on top. Again, you will either be given a molecule with a really short chain or a really long chain, and so the distinction of whether they will be soluble or insoluble will be easy.

That’s because the bigger the molecule the less polar it becomes, as the polar part of the molecule (-OH for alcohols, -NH2 for amines and C=O for compounds with carbonyl groups) is drowned out by the longer non-polar carbon chain. So, these large molecules are insoluble in water.

STOP AND CHECK:


Why alkanes, alkenes and alkynes are insoluble in water. What will happen when you mix a haloalkane with water. Why small carboxylic acids and amines are soluble in water but large alcohols

are insoluble in water.




Quick Questions

Explain the properties of alkanes, alkenes and alkynes, and any differences between them.

Discuss the properties of haloalkanes based on its functional group. Discuss the properties of alcohols (and diols) based on their functional group. Discuss the properties of carboxylic acids based on its functional group. Discuss the properties of amines based on its functional group. Discuss the properties of esters, amides, acyl chlorides, ketones and aldehydes

based on their functional group. Compare the properties of polar organic molecules with non-polar ones, giving

reasons for any differences.

IDENTIFICATION TESTSPretty much all of the organic compounds are colourless, which is both boring and dangerous. Who knows, maybe you pick up the wrong colourless solution and blow up the lab… Therefore, there needs to be a way to quickly make sure you’ve got the right compound, which is where identification tests come in.

So, what do you need to know to prevent a chemical explosion?

How to use red and blue litmus paper to tell if something is acidic, basic or neutralHow to separate your primary alcohols from secondary and tertiary alcohols using dichromate or permanganate solution How to use bromine water to tell if you’re dealing with alkanes or alkenes How to use Benedict’s solution, Fehling’s Solution or Tollens Reagent to distinguish aldehydes from ketones. The reaction of water with acyl chlorides.

Red and Blue Litmus Paper

It’s time to have a look at litmus paper. These bad boys of junior science are used to determine whether a solution is acidic, basic or neutral.

Litmus paper comes in two flavours: red and blue

If we throw some blue litmus paper into a basic solution, nothing happens. But, add it to an acidic solution and BAM! It goes through a transformation and comes out totally

?



red. The opposite happens with red litmus paper. It stays true to itself in acidic solution, but goes blue when soaked in basic solution.

This means that carboxylic acids, our organic acids, will turn blue litmus paper red and amines, our organic bases, will turn red litmus paper blue.

Let’s not forget about neutral solutions, like alcohols, haloalkanes, alkanes, alkenes and alkynes. Red litmus paper stays red and blue litmus paper stays blue in neutral solutions.

base

acid

neutral

base

acid

neutral

STOP AND CHECK:


What colour red and blue litmus paper will turn in the presence of an acidic solution.

What colour red and blue litmus paper will turn in the presence of a basic solution.

What colour red and blue litmus paper will turn in the presence of a neutral solution.


Distinguishing between Different Types of Alcohols

Remember, primary alcohols can be oxidised to carboxylic acids (first to aldehydes and then to carboxylic acids but if we just squirt a bunch of oxidising agent into a primary alcohol it will go all the way to the carboxylic acid) and secondary alcohols can be oxidised to ketones, but tertiary alcohols just can’t be bothered.

They’ve got the side chain on the same carbon as the hydroxyl group, and they’re just not going go to all the effort of removing that side chain just to add another oxygen atom.



The difference in their reactivity actually comes in handy as it allows us to distinguish alcohols from each other

In order to oxidise primary alcohols or secondary alcohols, strong oxidants must be added.

The two most common reagents are acidified dichromate solution (H+/Cr2O72−) and

acidified permanganate solution (H+/MnO4−). To tell whether an alcohol has been oxidised, a colour change will be observed:

Orange acidified dichromate solution will be reduced to green chromium ions (Cr3+).

primary/secondary alcohol

Cr2O72-

tertiary alcohol

Cr2O72-

Cr3+

Cr2O72-

Purple acidified permanganate solution will be reduced to colourless (or pale pink) manganese ions (Mn2+).

primary alcoholor secondary

AND

MnO4– Mn2+

tertiary alcohol

MnO4– MnO4

–

So, we can see that distinguishing primary and secondary alcohols from tertiary alcohols is easy enough. We will see no colour changes - acidified permanganate will remain purple and dichromate will remain orange - when added to tertiary alcohols.



How do we tell the difference between primary and secondary alcohols?

When primary alcohols are oxidised they are first oxidised to aldehydes and then to carboxylic acids, while secondary alcohols are oxidised to ketones.

As mentioned before, if we just squirt in some of our oxidising agent willy-nilly into our aldehyde solution we will form our carboxylic acid. We can tell the difference between a ketone and a carboxylic acid by doing the litmus test we described earlier as ketones are neutral but carboxylic acids are acidic.

STOP AND CHECK:


What is formed when primary alcohols are oxidised. The colour change that occurs when dichromate solution is added to a primary

alcohol and to a secondary or tertiary alcohol. What is formed when dichromate reacts with a primary alcohol. The colour change that occurs when permanganate solution is added to a

primary alcohol and to a secondary or tertiary alcohol. What is formed when permanganate reacts with a primary alcohol. Why dichromate and permanganate don’t react with tertiary alcohols.


Bromine Water

Alkanes and alkenes are annoyingly similar, as they both contain just carbon and hydrogen atoms. It’s a bit like seeing a cookie which looks like it could be chocolate chip, or, heaven forbid, raisin. Thankfully we have bromine water, a orange-brown solution, to solve the mystery.

Both alkanes and alkenes undergo a reaction with bromine water to form a bromoalkane (a haloalkane)

But, alkanes and alkenes are a little bit different in how they react.

Alkenes react straightaway, via an addition reaction, with no worries at all.

Alkanes, however, need a bit of help from UV light. And even then, the reaction is quite slow.



When bromine water reacts, the solution loses its colour as the colourless bromoalkane forms

So, to solve the mystery of the unknown solution, add bromine water without UV light and see whether the yellow-brown colour disappears.

alkene

Br2CH3- CH2- CH2- CH2- CH2- CH(Br) - CH2- Br

+ CH3- CH2- CH2- CH2- CH2- CH = CH2

alkane

Br2 Br2

+ CH3- CH2- CH2- CH2- CH2- CH2- CH3 + CH3- CH2- CH2- CH2- CH2- CH2- CH3

STOP AND CHECK:


What happens to bromine water when added to: - An alkene - An alkane without UV light.




DISTINGUISHING ALDEHYDES AND KETONESTwo reactions involving pretty colour changes can be used to distinguish aldehydes and ketones. In both cases, ketones don’t react so nothing exciting happens! The magic occurs when you have yourself an aldehyde:

Benedict’s and Fehling’s Solution

Benedict’s and Fehling’s solutions are exciting names for a solution with Cu2+ ions as the main ingredient

Throw some of this solution onto an aldehyde, and the aldehyde is oxidised to a carboxylic acid.

When this happens the Cu2+ ions are reduced to Cu+ ions, which reacts with oxygen to form Cu2O, a red-brown precipitate from the once beautiful blue solution.

Chuck it on a ketone and nothing happens

The ketone can’t be oxidised any further and so you’re stuck with the nice blue solution of Cu2+ ions.

STOP AND CHECK:


What Benedict’s/Fehling’s solution contains. What you’ll see when you add an aldehyde and a ketone to

Benedict’s/Fehling’s solution.


Tollens Reagent (Silver Mirror Test)

Tollens Reagent is a solution containing silver ions (Ag+)

When added to an aldehyde the aldehyde is again oxidised to a carboxylic acid.

This means that the Ag+ ions must be reduced and you end up with elemental silver, Ag. This is the same silver you’d use to make some pretty jewellery or a second-place Olympic medal.



When this is produced the silver precipitate coats the surface of the flask or container, forming a mirror-like surface.

With ketones unwilling to oxidise, no cool mirror is produced

If you’re still not convinced you’ve managed to tell the difference between the aldehyde and the ketone, other oxidation reactions involving colour changes – using either acidified permanganate solution, MnO4

−/H+, or acidified dichromate solution, Cr2O7

2−/H+ – can also be used as only aldehydes can be oxidised. As you’d expect, the ketones sit there like and do nothing.

Be careful though! Using acidified dichromate or permanganate solutions would also react with alcohols and so wouldn’t be suitable to help you tell the difference between aldehydes and alcohols. But, Benedict's solution, Fehling’s solution and Tollens reagent won’t react with alcohols.

STOP AND CHECK:


What Tollens Reagent contains. What you’ll when you add an aldehyde and a ketone with Tollens Reagent.


Acyl Chlorides and Water

We’ve talked a lot about specific reagents to test for certain types of organic molecules, but it seems acyl chlorides have been missed out.

Sometimes when you are given a handful of organic molecules and asked how to identify them, often a process of elimination can be used where the remaining molecule doesn’t need to be specifically tested.

But! There’s a simple test that can be used to test for acyl chlorides.

Acyl chlorides react vigorously with water

When water is added there will be an immediate, visual reaction. This is not seen when water is added to the other types of organic molecules - they might react with water but they don’t react vigorously.

Unfortunately this is not quite enough to prove that the molecule in question is an acid



chloride. For that we would need to do some extra tests. If you look back at the acyl chlorides section you will see that when we react acyl chlorides with water we get a carboxylic acid and HCl gas being produced.

If we test the gas that comes off of that reaction with damp blue litmus paper (the damp part is really important) and it turns red, that shows us that our HCl gas is present. We could also just test the flask with litmus to see if it is acidic, which it should be since we made a carboxylic acid.

STOP AND CHECK:


How water can be used to detect acyl chlorides. What acyl chlorides produce when they are reacted with water.


Quick Questions

In the lab, there are 5 beakers containing: ethanol, ethanoic acid, ethanamine, hexane and hex-1-ene. However, there are no labels. Using just water, litmus paper and bromine water, how can each solution be identified? In the lab, there are 3 alcohol compounds that have no labels. The 3 alcohol compounds are methylpropan-2-ol, butan-1-ol and butan-2-ol. How could these be distinguished from one another? How can propanal and propanone be distinguished from one another? How can prop-1-amine (1, aminopropane) and propanamide be told apart from each other.

?



KEY TERMSAddition Reaction:

A reaction involving the breaking of a double (or triple) bond, and the addition of new atoms or atom groups to the organic compound.

Branched Chain Isomer: Structural isomers which differ in the composition of the carbon backbone, due to the presence of branched groups attached to the main carbon chain (carbon backbone).

Elimination Reaction: A reaction involving the removal of atoms or atom groups from an organic compound, and the formation of a double bond between two carbon atoms in the compound.

Functional Group Isomers: Structural isomers that have different functional groups from one another (but are still composed of the same number and type of atoms).

Markovnikov’s Rule: (For major/minor products of addition reactions) the hydrogen atom is added to the carbon with the most hydrogen atoms already attached. “The rich get richer”.

Oxidation reaction: In organic chemistry this can be thought of “adding more bonds to oxygen”.

Polymer: A large molecule composed of small, repeating units, called monomers.

Positional Isomers: Structural isomers that differ in the position of their branched or functional groups. In other words, they differ in which carbon atoms their branched/functional groups are attached to.

Reduction reaction: In organic chemistry we can think of reduction as removing bonds to oxygen.

Reverse Markovnikov’s Rule: (For major/minor products of elimination reactions) the hydrogen atom is removed from the carbon with the least hydrogen atoms already attached. “The poor get poorer”.

This is also called Saytseff’s Rule.



Structural Isomer: Isomers with the same molecular formula but different structural formula. Structural isomers are also called constitutional isomers.

Substitution Reaction: An organic reaction involving the removal of one atom or a group of atoms (functional group) from an organic compound, and the addition of a new atom or group of atoms. In other words, it involves one group being swapped with another.

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ORGANIC COMPOUNDS - Home - StudyTime NZ · 2019. 7. 18. · Level 3 hemistr Organic Compounds Organic Compounds with just Carbon and Hydrogen With just two types of atoms, and only