Organic Chemistry. Introduction Organic chemistry is the study of carbon and its compounds. The major sources of carbon are the fossil fuels petroleum,

Organic Chemistry

Introduction

• Organic chemistry is the study of carbon and its compounds.

• The major sources of carbon are the fossil fuels petroleum, natural gas, and coal.

• Currently, about 7 million organic compounds account for about 90% of all known substances.

• Each year, over 50,000 new organic compounds are synthesized.

Introduction, Continued

• A hydrocarbon is a compound that contains only carbon and hydrogen.

• A hydrocarbon derivative is a compound derived from a hydrocarbon, but containing other elements, such as fluorine, nitrogen, and oxygen.

• There are two types of hydrocarbons:1. Saturated hydrocarbons

2. Unsaturated hydrocarbons

4Chapter 19© 2011 Pearson Education, Inc.

• Hydrocarbons– Compound made up entirely of carbon and

hydrogen – Majority of petroleum components– Carbon always forms four bonds.– Hydrogen always forms one bond.


• Petroleum– Primary use as a fuel– Used for many other products as well

• Examples are fertilizers, insecticides, plastics, food preservatives, paints, inks, lubricants, detergents, solvents, and medicines.


• Chains of carbon– Chain length—number of carbon atoms in the

longest continuous chain

Chain length of eight


• Linear hydrocarbon– Each of the nonterminal carbons are attached to

two other carbon atoms– Does not form a straight line of carbons since the

bonding angle is 109.5°


• Branched hydrocarbon– At least one carbon atom is attached to more than

two other carbon atoms.– Small branch forming off the main carbon chain


For the following molecule what is the length of the

main chain and what is the length of the branch

chain?


For the following molecule what is the length of the

main chain and what is the length of the branch

chain?

Main chain: six carbons

Branch chain: two carbons


• Line drawings– Representation showing only the C—C bonds,

omitting the H bonds– Bonds not shown are assumed to be H bonds.


• Double and triple bonds are shown with multiple dashes.


What would the molecular formula be for each of

the following molecules:


What would the molecular formula be for each of

the following molecules:

(a) C7H16

(b) C6H12

(c) C6H6

Saturated Hydrocarbons

• A saturated hydrocarbon has only single bonds between the carbon atoms.

• Carbon can form four single covalent bonds to other atoms.

• A saturated hydrocarbon with only single bonds belongs to the alkane family.

Unsaturated Hydrocarbons

• An unsaturated hydrocarbon has either a double or triple bond between two carbon atoms.– If it has a double bond, it is an alkene (b).

– If it has a triple bond, it is an alkyne (c).

• An aromatic hydrocarbon has a benzene ring. A benzene ring is a six-membered ring of carbon atoms with alternating single and double bonds (d).

Classification of Hydrocarbons

• Below is a flowchart for the classification of hydrocarbons.


Structural Isomers

• Two compounds with the same molecular formula, but different structural formulas are isomers.

• Butane has the formula C4H10. We can draw the formula in two ways:

CH3CH2CH2CH3 and CH3CH(CH3)CH3

• The two isomers have different physical properties.


Structural Isomers

• Isomers– Compounds with the same formula, but different

structures

Alkanes

• Alkanes are a family of compounds whose names end in the suffix -ane. They are saturated hydrocarbons.

• They each have the same general molecular formula: CnH2n+2.

– The fifth member of the alkane family, pentane, has 5 carbon atoms and 12 (2 x 5 + 2 = 12) hydrogen atoms, C5H12.


Alkanes

Number of Carbons Present in Main Chain

Alkane Family

• The lighter alkanes (1–10 carbons) are used as fuels, whereas the larger alkanes (20–40 carbons) are solids used to make waxes and candles.

Alkyl and Aryl Groups

• When a hydrogen is removed from an alkane, an alkyl group results.

CH4 – H = CH3– methane methyl group

CH3-CH3 – H = CH3-CH2– ethane ethyl group

• When we remove the hydrogen atom, the name -ane suffix is changed to -yl.

Alkyl and Aryl Groups, Continued

Guidelines for Naming Alkanes

1. Name an alkane for its longest continuous carbon chain regardless of the branches.

2. Number the longest continuous chain starting from the end closest to the first branch on the chain.

3. Indicate the position of the alkyl groups by name and number.

4. If there are two or more of the same group attached to the chain, use the prefixes di-, tri-, tetra-, etc.

Nomenclature of Alkanes

• What is the name of the following alkane?

• The longest chain has five carbons, so it is a pentane derivative. The methyl group is in the 2 position.

• The name is 2-methylpentane.

Nomenclature of Alkanes, Continued

• What is the name of the following alkane?

• The longest chain has six carbons, so it is a hexane derivative. The methyl groups are in the 2, 4, and 4 positions.

• The name is 2,4,4-trimethylhexane.

Alkane Reactions

• The C–C and C–H bonds in alkanes are very strong and are unreactive at room temperature.

• At high temperatures, alkanes burn rapidly in the presence of oxygen. This is a combustion reaction.

CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)

• The products of a combustion reaction are carbon dioxide and water.

Alkene and Alkyne Formulas

• Alkenes contain one or more double bonds. The general molecular formula for an alkene with one double bond is CnH2n.

– The fifth member of the alkene family, pentene, has 5 carbon atoms and 10 (2 x 5 = 10) hydrogen atoms, C5H10.

• Alkynes contain one or more triple bonds. The general molecular formula for an alkyne with one double bond is CnH2n-2.

– The fifth member of the alkyne family, pentyne, has 5 carbon atoms and 8 (2 x 5 – 2 = 8) hydrogen atoms, C5H8.

Alkene Family

• Butene, C4H8, has two structural isomers. The double bond can be between the first and second carbon or between the second and third carbon.

Guidelines for Naming Alkenes

1. Name an alkene for its longest continuous carbon chain that contains the double bond. The name is the same as the alkane with the -ane suffix changed to -ene.

2. Number the longest continuous chain starting from the end closest to the double bond.

3. Indicate the position of the attached alkyl groups by name and number.


Nomenclature of Alkenes

• What is the name of the following alkene?

• The longest chain with the double bond has six carbons, so it is a hexene derivative. The double bond is the second bond, so it is a hex-2-ene. The methyl groups are in the 3, 5, and 5 positions.

• The name is 3,5,5-trimethylhex-2-ene.

Alkyne Family

• Butyne, C4H6, has two structural isomers. The triple bond can be between the first and second carbon or between the second and third carbon.

Guidelines for Naming Alkynes

1. Name an alkene for its longest continuous carbon chain that contains the triple bond. The name is the same as the alkane, with the -ane suffix changed to -yne.

2. Number the longest continuous chain starting from the end closest to the triple bond.

3. Indicate the position of the attached alkyl groups by name and number.


Nomenclature of Alkynes

• What is the name of the following alkyne?

• The longest chain with the triple bond has four carbons, so it is a butyne derivative. The triple bond is the first bond, so it is a but-1-yne. The methyl group is in the 3 position.

• The name is 3-methylbut-1-yne.

Reactions of Alkenes and Alkynes

• In addition to combustion reactions, alkenes and alkynes also undergo addition reactions. The double or triple bond can add atoms. There are two types:

1. Hydrogenation

CH≡CH(g) + H2(g) → CH2=CH2(g)

2. Halogenation

CH2=CH2(l) + Br2(l) → CH2Br-CH2Br(l)

Polymerization Reactions

• A polymer is a giant molecule made up from many small molecules (monomers) joined in a long chain.

• Ethylene, CH2=CH2, can react to give polyethlyene.

• We represent the polymer as [-CH2-CH2-]n.

n CH2=CH2 → [-CH2-CH2-]n

monomer polymer

Arenes• Arenes contain a benzene ring.

• Arenes are also called aromatic compounds because of their fragrant smell.

• The formula for benzene is C6H6, and it has a cyclic structure.

• The double bonds are delocalized, and benzene is often written with a circle in the middle.

Isomers of a Disubstituted Benzene• If we replace two of the hydrogens on benzene

with chlorines, we have dichlorobenzene, C6H4Cl2.• The chlorine atoms can be arranged in the

following three different ways:

Isomers of a Disubstituted Benzene, Continued

• If the chlorines are on adjacent carbons, we have ortho-dichlorobenzene.

• If the chlorines are separated by one carbon, we have meta-dichlorobenzene.

• If the chlorines are opposite each other, we have para-dichlorobenzene.

Hydrocarbon Derivatives

• There are millions of organic compounds.

• We can categorize them into classes of compounds.

• Each of the classes has a specific functional group. A functional group is a set of atoms that gives a class of compounds its characteristics.

• There are 10 classes: five without a carbonyl group and five with a carbonyl group (C=O).

Non-Carbonyl Hydrocarbon Derivatives

• Here are the basic hydrocarbon classes. R is an alkyl group and Ar is an aryl group.

Carbonyl Hydrocarbon Derivatives

Organic Halides

• If a halogen atom (F, Cl, Br, and I) replaces a hydrogen atom in a hydrocarbon, the new compound is an organic halide.

• Organic halides are used primarily as household and industrial solvents.

• They are found in many pesticides.

• They are essentially nonpolar molecules with low boiling points and properties similar to those of alkanes.

Alcohols and Phenols

• When an –OH group replaces a hydrogen atom on an alkane, the result is an alcohol.

• When an –OH replaces a hydrogen atom on an arene, the resulting molecule is a phenol.

• The –OH group is called a hydroxyl group.

• The names of alcohols are derived from the parent alkane by changing the -ane ending to an -ol suffix.

– For example, CH3CH2OH is ethanol.

Alcohols and Phenols, Continued• Most alcohols are quite water soluble because of

the polar –OH group, which allows for hydrogen bonding.

• Alcohols have higher boiling points than their parent alkanes.

Ethers

• Organic molecules with two hydrocarbon groups attached to an oxygen are ethers, R–O–R.

• Ethers are usually named by indicating the two groups attached to the oxygen.

• Ethers do not hydrogen bond, and their properties lie between those of alkanes and alcohols.

Amines

• If an alkyl or aryl group replaces a hydrogen in ammonia, an amine results: R–NH2.

• Amines are often referred to by their common names, indicating the alkyl group present.

• Most amines are polar due to their ability to hydrogen bond.

Aldehydes

• Aldehydes contain a carbonyl (C=O) group and are polar.

• In an aldehyde, the carbonyl group is attached to a hydrogen and an alkyl or aryl group, R–CHO.

• The name of an aldehyde is derived from its parent alkane by changing the -ane to an -al suffix.

Ketones

• Ketones also contain the carbonyl group and are generally polar.

• Ketones have two alkyl or aryl groups attached to the carbonyl group, R–COR'.

• Ketones are named for their parent alkane.

Carboxylic Acids

• In a carboxylic acid, a hydroxyl group and alkyl or aryl group is bonded to a carbonyl group, RCOOH.

• This group, –COOH, is a carboxyl group.

• Acetic acid, CH3COOH, is a major component of vinegar and gives it its sour taste.

• Carboxylic acids are named from their parent alkane by dropping the -ane ending and replacing it with a -oic acid suffix.

Carboxylic Acids, Continued

• Carboxylic acids are polar since the carboxyl group, –COOH, can form hydrogen bonds.

• They have similar properties to alcohols with high boiling points and good water solubility.

Esters

• An ester has an –R and an –OR group bonded to a carbonyl group, RCOOR.

• Esters typically have a pleasant, fruity odor.

• They are slightly polar.

• They are typically formed from the reaction of an alcohol with a carboxylic acid.

Amides

• In amides, a carbonyl group is attached to an alkyl or aryl group and an –NH2 group.

• Amides are formed from the reaction of a carboxylic acid with ammonia.

• They are polar molecules with properties similar to those of carboxylic acids.

Chapter Summary

• Organic chemistry is the study of compounds that contain carbon.

• Hydrocarbons contain only hydrogen and carbon.

• Saturated hydrocarbons have only single carbon–carbon bonds.

• Unsaturated hydrocarbons have double or triple carbon–carbon bonds.

• Aromatic hydrocarbons have a benzene ring.

Chapter Summary, Continued

• Alkenes have at least one carbon–carbon double bond.

• Alkynes have at least one carbon–carbon triple bonds.

• Arenes contain a benzene ring.

• Hydrocarbon derivatives have a functional group in addition to the hydrocarbon function. They are summarized on the next slide.

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Organic Chemistry. Introduction Organic chemistry is the study of carbon and its compounds. The major sources of carbon are the fossil fuels petroleum,