Chem 150 Unit 2 - Hydrocarbons & Functional Groups

Chem 150Chem 150Unit 2 - Hydrocarbons & Unit 2 - Hydrocarbons &

Functional GroupsFunctional Groups

Organic chemistry is the chemistry of carbon. Organic chemistry is the chemistry of carbon. The name “organic” reflect the fact that organic The name “organic” reflect the fact that organic molecules are derived from living organisms. In molecules are derived from living organisms. In this unit will start by looking at four families of this unit will start by looking at four families of

organic molecules that are grouped together as organic molecules that are grouped together as the hydrocarbons. We will also look at some the hydrocarbons. We will also look at some

functional groups that define some of the other functional groups that define some of the other families of organic molecules.families of organic molecules.

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Organic ChemistryOrganic Chemistry

Organic chemistry is the chemistry of carbon.Organic chemistry is the chemistry of carbon.• There are three forms of pure carbonThere are three forms of pure carbon

• DiamondDiamond

• GraphiteGraphite

3

Organic ChemistryOrganic Chemistry

Organic chemistry is the chemistry of carbon.Organic chemistry is the chemistry of carbon.• There are three forms of pure carbonThere are three forms of pure carbon

• BuckminsterfullereneBuckminsterfullerene“Bucky Balls”“Bucky Balls”

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HydrocarbonsHydrocarbons

• Organic molecules contain carbon combined with other Organic molecules contain carbon combined with other elements.elements.

• Organic molecules are grouped into familiesOrganic molecules are grouped into families• Members of a family share common structural, physical, and chemical Members of a family share common structural, physical, and chemical

characteristics.characteristics.

• There are four families that contain molecules made of only There are four families that contain molecules made of only carbon and hydrogen.carbon and hydrogen.

• HydrocarbonsHydrocarbons• AlkanesAlkanes

• AlkenesAlkenes

• AlkynesAlkynes

• AromaticsAromatics

5

HydrocarbonsHydrocarbons

6

AlkanesAlkanes

Alkanes are hydrocarbons that contain only carbon-carbon Alkanes are hydrocarbons that contain only carbon-carbon single bonds.single bonds.• Every carbon atom participates in 4 single bonds, either to Every carbon atom participates in 4 single bonds, either to

another carbon or to a hydrogen.another carbon or to a hydrogen.• Every hydrogen atom is bonded to a carbon by a single Every hydrogen atom is bonded to a carbon by a single

bond.bond.

7

AlkanesAlkanes

Alkanes are hydrocarbons that contain only carbon-carbon Alkanes are hydrocarbons that contain only carbon-carbon single bonds.single bonds.

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AlkanesAlkanes

• Alkanes in which the carbons are connected in a straight Alkanes in which the carbons are connected in a straight chain are called chain are called normal alkanesnormal alkanes..

• Alkanes that are branched are called Alkanes that are branched are called branched chain branched chain alkanesalkanes..

C C C C C C

H

H

H

H H H H H

H

HHHHH

C C C C C H

H

H

H

C

H H H

HHHH

H

H

H

n-hexanen-hexane

2-methyl-pentane2-methyl-pentane

AlkanesAlkanes

For a discusion on the structure of alkanes,For a discusion on the structure of alkanes,see the Unit 2see the Unit 2Elaboration - Alkane Structure

http://www.chem.uwec.edu/Chem150_S07/elaborations/unit2/unit2-a-alkanes.html

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AlkanesAlkanes

• Alkanes, along with the other hydrocarbons, are non-polar.Alkanes, along with the other hydrocarbons, are non-polar.

• They interact with each other only through London They interact with each other only through London dispersion forces.dispersion forces.

• This is why they have relatively low boiling and melting This is why they have relatively low boiling and melting points.points.

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They interact with each other only through London dispersion They interact with each other only through London dispersion forces.forces.• Note how the boiling points increase with molecular weight.Note how the boiling points increase with molecular weight.

AlkanesAlkanes

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Molecule in the NewsMolecule in the News

13

Molecule in the News:MelamineMolecule in the News:Melamine

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http://www.cbc.ca/health/story/2007/09/06/additives-lancet.html?ref=rss

http://www.medpagetoday.com/Psychiatry/ADHD-ADD/tb/6610

Organic Molecules in the News!!

CarmoisineCarmoisine

Quinoline yellowQuinoline yellowSodium benzoateSodium benzoate

http://www.cbc.ca/health/story/2007/09/06/additives-lancet.html?ref=rss

http://www.medpagetoday.com/Psychiatry/ADHD-ADD/tb/6610

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Alkanes, cannot be named based on their molecular formulasAlkanes, cannot be named based on their molecular formulas• For example, all of the molecules shown below share the For example, all of the molecules shown below share the

same molecular formula, Csame molecular formula, C66HH1414

((hexacarbon tetradecahydridehexacarbon tetradecahydride?)?)

Alkanes

C C C C C C

H

H

H

H H H H H

H

HHHHH

C C C C C H

H

H

H

C

H H H

HHHH

H

H

H

n-hexanen-hexane


C C C C C H

H

H

H

C

H H

HHHH

H

H

H

H

C C C C

H

H

H

C

H H

HH

C

H

H

H

H

H

H

H

C C C C

H

H

H

C

H

HH

C

H

H

H

H

H

H

H

H

3-methyl-pentane3-methyl-pentane 2,2-dimethylbutane2,2-dimethylbutane 2,3-dimethylbutane2,3-dimethylbutane

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Organic chemists use a systematic set of rules, called the Organic chemists use a systematic set of rules, called the IUPAC rules, to name organic molecules based on their IUPAC rules, to name organic molecules based on their structural formulas instead of their chemical formulas.structural formulas instead of their chemical formulas.

Alkanes

C C C C C C

H

H

H

H H H H H

H

HHHHH

C C C C C H

H

H

H

C

H H H

HHHH

H

H

H

n-hexanen-hexane


C C C C C H

H

H

H

C

H H

HHHH

H

H

H

H

C C C C

H

H

H

C

H H

HH

C

H

H

H

H

H

H

H

C C C C

H

H

H

C

H

HH

C

H

H

H

H

H

H

H

H


AlkanesAlkanes

For a discussion on naming alkanes,For a discussion on naming alkanes,see the Unit 2see the Unit 2Elaboration - Naming Alkanes

http://www.chem.uwec.edu/Chem150_S07/elaborations/unit2/unit2-b-naming-alkanes.html

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When two or more molecules share the same molecular When two or more molecules share the same molecular formula, but have different atomic connections, they are formula, but have different atomic connections, they are called called constitutional isomersconstitutional isomers..

Constitutional Isomers

C C C C C C

H

H

H

H H H H H

H

HHHHH

C C C C C H

H

H

H

C

H H H

HHHH

H

H

H

n-hexanen-hexane


C C C C C H

H

H

H

C

H H

HHHH

H

H

H

H

C C C C

H

H

H

C

H H

HH

C

H

H

H

H

H

H

H

C C C C

H

H

H

C

H

HH

C

H

H

H

H

H

H

H

H


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Question (Clicker)

Which of the following is a constitutional isomer of this Which of the following is a constitutional isomer of this molecule:molecule:

H3C CH

CH3

CH

CH3

CH2 CH2 CH3

H3C CH

CH3

CH

CH3

CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3

CH3

CH

CH3

CH

CH3

CH2

H2C CH3

A)A)

B)B)

C)C)

D)D)C C C C

H

H

H

C

H

HH

C

H

H

H

H

H

H

H

H

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ConformationsConformations

Carbon-carbon single bonds are free to rotateCarbon-carbon single bonds are free to rotate

• This leads to different shapes for some moleculesThis leads to different shapes for some molecules

• These should not be confused with isomers.These should not be confused with isomers.

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All of the 3-dimensional models shown below are for the All of the 3-dimensional models shown below are for the n-n-butanebutane..• They were generated by rotating the central carbon-carbon They were generated by rotating the central carbon-carbon

bond.bond.• They all share the same structural formula.They all share the same structural formula.

C C C C

H

H

H

HHH

H H H

H

22


All of the 3-dimensional models shown below are for the All of the 3-dimensional models shown below are for the n-n-butanebutane..• They were generated by rotating the central carbon-carbon They were generated by rotating the central carbon-carbon

bond.bond.

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Switching from one conformation to another Switching from one conformation to another does notdoes not require require the breaking and making of covalent bonds.the breaking and making of covalent bonds.

• Switching from one isomer to another Switching from one isomer to another doesdoes require the require the breaking and making of covalent bonds.breaking and making of covalent bonds.

C C C

C

H

H H

H

H

H H

H

H

H

C C C C

H

H

H

HHH

H H H

H

n-butanen-butane 2-methylpropane2-methylpropane


For a discussion on conformations,For a discussion on conformations,see the Unit 2see the Unit 2Elaboration - Conformations

http://www.chem.uwec.edu/Chem150_S07/elaborations/unit2/unit2-c-conformations.html

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Question (Clicker)Question (Clicker)

True or False? Constitutional isomers have the same IUPAC True or False? Constitutional isomers have the same IUPAC name.name.

• TrueTrue• FalseFalse

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Question (Clicker)Question (Clicker)

True or False? The different conformations of an alkane have True or False? The different conformations of an alkane have the same IUPAC name.the same IUPAC name.

• TrueTrue• FalseFalse

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CycloalkanesCycloalkanes

When there are three or more carbons in a straight chain, the When there are three or more carbons in a straight chain, the ends can be joined to make rings.ends can be joined to make rings.

• In naming these molecules, the prefix In naming these molecules, the prefix cyclocyclo- is used to - is used to indicate the ring:indicate the ring:

• Skeletal structural formulas are used to represent the rings Skeletal structural formulas are used to represent the rings in structural formulas:in structural formulas:

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In naming these molecules, the prefix In naming these molecules, the prefix cyclocyclo- is used to - is used to indicate the ring:indicate the ring:

Cycloalkanes

cyclopropane

cyclobutane

cyclopentane

cyclohexane

C3H6

C4H8

C5H10

C6H12

R

R

R

R

cyclopropyl-

cyclobutyl-

cyclopentyl-

cyclohexyl-

As Parent ChainAs Parent Chain As Substituent GroupAs Substituent Group

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The carbon-carbon single bonds for the carbons in a ring are The carbon-carbon single bonds for the carbons in a ring are no longer free to rotate.no longer free to rotate.

• This leads to a new type of isomerThis leads to a new type of isomer• Since the two structures share the same name, they are Since the two structures share the same name, they are

not constitutional isomers.not constitutional isomers.

Cycloalkanes

CH3 CH3 CH3 CH3

H

H HH

CH3CH3

H

HH

H HH

H

H

HH

CH3H

CH3

HH

H H

1,2-dimethylcyclohexane 1,2-dimethylcyclohexane

30

Isomers which share the same atomic connections, and Isomers which share the same atomic connections, and therefore, the same IUPAC name are called therefore, the same IUPAC name are called stereoisomers.stereoisomers.• When this occurs due to restricted rotation about a When this occurs due to restricted rotation about a

covalent bond, they are called covalent bond, they are called geometric isomersgeometric isomers• The prefix The prefix cis-cis- and and trans-trans- are used to distinguish geometric are used to distinguish geometric

isomers.isomers.

Cycloalkanes

CH3 CH3 CH3 CH3

H

H HH

CH3CH3

H

HH

H HH

H

H

HH

CH3H

CH3

HH

H H

cis-1,2-dimethylcyclohexane trans-1,2-dimethylcyclohexane

31

Questions

Draw the condensed structural formulas for the following Draw the condensed structural formulas for the following molecules:molecules:

A)A) 1-ethyl-2-methylcyclopentane1-ethyl-2-methylcyclopentane

B)B) 1,1-dimethylcyclobutane1,1-dimethylcyclobutane

C)C) 1,1-dimethyl-2-propylcyclopropane1,1-dimethyl-2-propylcyclopropane

Do any of these molecules have Do any of these molecules have cis-cis- and and trans-trans- geometric geometric isomers?isomers?

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Alkenes, Alkynes & Aromatic CompoundsAlkenes, Alkynes & Aromatic Compounds

The remaining three families of hydrocarbons are The remaining three families of hydrocarbons are unsaturatedunsaturated..

• Alkanes are Alkanes are saturatedsaturated, which means they contain the , which means they contain the maximum number of hydrogens per carbon.maximum number of hydrogens per carbon.

• For alkanes CFor alkanes CnnHH(2n+2)(2n+2)

• Alkenes, Alkynes Alkenes, Alkynes andand Aromatics Aromatics are are unsaturatedunsaturated, which , which means they contain less than the maximum number of means they contain less than the maximum number of hydrogens per carbon.hydrogens per carbon.

• Structurally, this means that they have carbon-carbon double or triple bondsStructurally, this means that they have carbon-carbon double or triple bonds

33


AlkenesAlkenes are hydrocarbons that contain at least 1 carbon- are hydrocarbons that contain at least 1 carbon-carbon double bond.carbon double bond.• Examples:Examples:

C CH

H

H

CH2 CH2 CH2 CH3

1-hexene

C CH

H

H

H

ethene(ethylene)

34


AlkynesAlkynes are hydrocarbons that contain at least 1 carbon- are hydrocarbons that contain at least 1 carbon-carbon triple bond.carbon triple bond.• Examples:Examples:

C CH CH2 CH2 CH2 CH3

1-hexyne

C CH H

ethyne(acetylene)

35


AromaticsAromatics are unsaturated ring molecules are unsaturated ring molecules• They are often drawn to look like alkenes, but they behave They are often drawn to look like alkenes, but they behave

much differently than alkenes.much differently than alkenes.• They have an alternating pattern of double and single They have an alternating pattern of double and single

bonds within a ring.bonds within a ring.• Benzene is an exampleBenzene is an example

36


The physical properties of all hydrocarbons are the sameThe physical properties of all hydrocarbons are the same

• The have essentially one noncovalent interaction, which The have essentially one noncovalent interaction, which isthe London dispersion force.isthe London dispersion force.

• They have no electronegative atoms and therefore haveThey have no electronegative atoms and therefore have

• No ion/ion interactionsNo ion/ion interactions

• No dipole/dipole interactionsNo dipole/dipole interactions

• No hydrogenbonding interactionsNo hydrogenbonding interactions

37


Naming of Alkenes and Alkynes work the same as for Naming of Alkenes and Alkynes work the same as for alkanes, with these added rules:alkanes, with these added rules:

• The parent chain must include both carbons in all double The parent chain must include both carbons in all double and triple bonds.and triple bonds.• Pick the longest chain that also contains all double and triple bondsPick the longest chain that also contains all double and triple bonds

• The The -ene-ene ending is used of alkenesending is used of alkenes

• The -The -yneyne ending is used for alkynes. ending is used for alkynes.

• The number of the first carbon in the double or triple bond is The number of the first carbon in the double or triple bond is included in the name to locate the double or triple bond.included in the name to locate the double or triple bond.• Number the parent chain from the end that is closes to the first double or triple Number the parent chain from the end that is closes to the first double or triple

bond.bond.

38


Naming of Aromatics is based on benzene:Naming of Aromatics is based on benzene:• When the molecule is build on benzene, the parent name When the molecule is build on benzene, the parent name

is “benzene”.is “benzene”.• There are also many common names used to describe There are also many common names used to describe

aromatic compounds.aromatic compounds.

39


Naming of Aromatics is based on benzene:Naming of Aromatics is based on benzene:• Aromatic compounds can contain multiple aromatic rings Aromatic compounds can contain multiple aromatic rings

40


Benzo(a)pyrene found in tobacco smoke is converted to Benzo(a)pyrene found in tobacco smoke is converted to carcinogenic products in the liver (see below) which link to carcinogenic products in the liver (see below) which link to DNA and cause mutations.DNA and cause mutations.

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Practice Quiz 1 KEYPractice Quiz 1 KEY

http://www.chem.uwec.edu/Chem150_S07/course/answers/C150-Quiz-1-key.swf



42


There are many aromatic molecules found in biologyThere are many aromatic molecules found in biology• Some aromatic compounds contain nitrogen and oxygen Some aromatic compounds contain nitrogen and oxygen

atomsatoms• For example, the nucleotide base Adenine, which is used For example, the nucleotide base Adenine, which is used

to make DNA and RNAto make DNA and RNA

N

N

N

NH2

43


Like cycloalkanes, some alkenes can have Like cycloalkanes, some alkenes can have ciscis and and transtrans isomersisomers

• This is due to restricted rotation about the double-bond.This is due to restricted rotation about the double-bond.

• Not all double bonds produce Not all double bonds produce ciscis and and transtrans isomers isomers• Each carbon participating in the double bond must have two different Each carbon participating in the double bond must have two different

substituents attached to themsubstituents attached to them

A ≠ B AND X ≠ Y

C CA

B

X

Y

44


Like cycloalkanes, some alkenes can have Like cycloalkanes, some alkenes can have ciscis and and transtrans isomersisomers

45

Alcohols, Carboxylic Acids & EstersAlcohols, Carboxylic Acids & Esters

In addition to the four families of hydrocarbons, there are also In addition to the four families of hydrocarbons, there are also many other families of organic molecules.many other families of organic molecules.

These other families include elements other than carbon and These other families include elements other than carbon and hydrogen.hydrogen.

• They exhibit a wide range of chemical and physical They exhibit a wide range of chemical and physical properties.properties.

• The families are distinguished by a group of atoms called a The families are distinguished by a group of atoms called a functional groupfunctional group

46


Functional GroupFunctional Group

““A functional group is an atom, group of atoms or bond that A functional group is an atom, group of atoms or bond that gives a molecule a particular set of chemical and physical gives a molecule a particular set of chemical and physical properties”properties”

47


The carbon-carbon double bonds found in alkenes is an The carbon-carbon double bonds found in alkenes is an example of a functional group.example of a functional group.

• A chemical property of a double is that it will absorb A chemical property of a double is that it will absorb hydrogen in the hydrogenation reaction.hydrogen in the hydrogenation reaction.

48

We look now at three families that are distinguished by a We look now at three families that are distinguished by a functional group that contains the element oxygen.functional group that contains the element oxygen.

AlcoholsAlcohols• Members of the alcohol family contain a Members of the alcohol family contain a hydroxyl grouphydroxyl group..• The hydroxyl group comprises an oxygen with one single The hydroxyl group comprises an oxygen with one single

bond to a hydrogen and another single bond to an alkane-bond to a hydrogen and another single bond to an alkane-type carbontype carbon


C C

H

H

H

H

H

O H hydroxyl grouphydroxyl group

An alkane-type carbon atomAn alkane-type carbon atom

ethanolethanol

49


Carboxylic acidsCarboxylic acids• Members of the carboxylic acid family contain a Members of the carboxylic acid family contain a carboxylic carboxylic

acid groupacid group• The carboxylic acid group comprises a hydroxyl group The carboxylic acid group comprises a hydroxyl group

connected to a carbonyl group:connected to a carbonyl group:


++C

O

O H C

O

O H

carbonyl groupcarbonyl group hydroxyl grouphydroxyl group carboxylic acid groupcarboxylic acid group

50


Carboxylic acidsCarboxylic acids• The present of the hydroxyl group next to the cabonyl The present of the hydroxyl group next to the cabonyl

group completely changes it properties.group completely changes it properties.• The alcohol hydroxyl group and the carboxylic acid hydroxyl group are The alcohol hydroxyl group and the carboxylic acid hydroxyl group are

chemically quite different, which is why molecules that have the carboxylic acid chemically quite different, which is why molecules that have the carboxylic acid group are placed in a separate family from the alcohols.group are placed in a separate family from the alcohols.

• Later in the semester we will learn about some of these chemical differences.Later in the semester we will learn about some of these chemical differences.

++C

O

O H C

O

O H

carbonyl groupcarbonyl group hydroxyl grouphydroxyl group carboxylic acid groupcarboxylic acid group

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Carboxylic acidsCarboxylic acids• The carboxylic acid group can be attached to a hydrogen, The carboxylic acid group can be attached to a hydrogen,

an alkane-type carbon, or an aromatic-type carbon:an alkane-type carbon, or an aromatic-type carbon:


methanoic acidmethanoic acid(formic acid)(formic acid)

propanoic acidpropanoic acid benzoic acidbenzoic acid

C OH

O

H C OH

O

CC

H

H

H

H

H C OH

O

52


EstersEsters• Chemically, esters can be synthesized by reacting a Chemically, esters can be synthesized by reacting a

carboxylic acid with and alcohol:carboxylic acid with and alcohol:


carboxylic carboxylic acidacid

alcoholalcohol esterester waterwater

C

O

O H H O C+ C

O

O C H O+ H

53


EstersEsters• Chemically, esters can be synthesize by reacting a Chemically, esters can be synthesize by reacting a

carboxylic acid with and alcohol:carboxylic acid with and alcohol:


C

O

O CH2CH2CH3 CH3

Carboxylicacid part

Alcoholpart

Ethyl propanoateEthyl propanoate

54

Carboxylic acidsCarboxylic acids• The carboxylic acid group can be attached to a hydrogen, The carboxylic acid group can be attached to a hydrogen,

an alkane-type carbon, or an aromatic-type carbon:an alkane-type carbon, or an aromatic-type carbon:

Alcohols, Carboxylic Acids & Esters

methanoic acidmethanoic acid(formic acid)(formic acid)

propanoic acidpropanoic acid benzoic acidbenzoic acid

C OH

O

H C OH

O

CC

H

H

H

H

H C OH

O

55

As we saw with the hydrocarbons, the physical properties of As we saw with the hydrocarbons, the physical properties of organic molecules depend on the noncovalent intermolecular organic molecules depend on the noncovalent intermolecular interactions which attract one one molecule to another.interactions which attract one one molecule to another.

• With hydrocarbons, there is only one type of noncovalent With hydrocarbons, there is only one type of noncovalent interaction:interaction:• Induced dipole/Induced dipole (London dispersion force)Induced dipole/Induced dipole (London dispersion force)

• The presence of the electronegative oxygen makes The presence of the electronegative oxygen makes alcohols, carboxylic acids and esters polar molecules, alcohols, carboxylic acids and esters polar molecules, these families, therefore, have at least two types of these families, therefore, have at least two types of noncovalent interactions:noncovalent interactions:• Induced dipole/Induced dipole (London dispersion force)Induced dipole/Induced dipole (London dispersion force)• Dipole/DipoleDipole/Dipole


56

As we saw with the hydrocarbons, the physical properties of As we saw with the hydrocarbons, the physical properties of organic molecules depend on the noncovalent intermolecular organic molecules depend on the noncovalent intermolecular interactions which attract one one molecule to another.interactions which attract one one molecule to another.

• Alcohols and Carboxylic acids also have a hydroxyl group Alcohols and Carboxylic acids also have a hydroxyl group with a hydrogen bonded to an oxygen. This allows them to with a hydrogen bonded to an oxygen. This allows them to form hydrogen bonds with each other. Therefore, form hydrogen bonds with each other. Therefore, carboxylic acids have at least three different noncovalent carboxylic acids have at least three different noncovalent interactions:interactions:• Induced dipole/Induced dipole (London dispersion force)Induced dipole/Induced dipole (London dispersion force)• Dipole/DipoleDipole/Dipole• Hydrogen bondHydrogen bond


57

To summarize, the types of noncovalent interact ions that To summarize, the types of noncovalent interact ions that each family can participate in include:each family can participate in include:

• Hydrocarbons (Alkanes, Alkenes, Alkynes & Hydrocarbons (Alkanes, Alkenes, Alkynes & Aromatics)Aromatics)• Induced dipole/Induced dipole (London dispersion force)Induced dipole/Induced dipole (London dispersion force)

• EstersEsters• Induced dipole/Induced dipole (London dispersion force)Induced dipole/Induced dipole (London dispersion force)• Dipole/DipoleDipole/Dipole

• Alcohols & Carboxylic acidsAlcohols & Carboxylic acids• Induced dipole/Induced dipole (London dispersion force)Induced dipole/Induced dipole (London dispersion force)• Dipole/DipoleDipole/Dipole• Hydrogen bondHydrogen bond


58

These interactions are illustrated in Figure 4.23 of your These interactions are illustrated in Figure 4.23 of your textbook.textbook.


alcoholsalcohols

carboxylic acidscarboxylic acids

estersesters

59

Boiling points are a good measure of the strength of the Boiling points are a good measure of the strength of the noncovalent interactions between molecules.noncovalent interactions between molecules.

• The stronger the interactions, the higher the boiling point will The stronger the interactions, the higher the boiling point will be.be.

• Since all molecules have the London dispersion interaction, Since all molecules have the London dispersion interaction, the boiling points of molecules is expected to increase with the boiling points of molecules is expected to increase with temperature.temperature.

• The next slide shows a chart using the data found in Table The next slide shows a chart using the data found in Table 4.7 of Raymond, in which the boiling points for alcohols, 4.7 of Raymond, in which the boiling points for alcohols, carboxylic acids and esters are plotted against molecular carboxylic acids and esters are plotted against molecular weight.weight.


60

Alcohols, Carboxylic Acids & Esters• As expected, the boiling points As expected, the boiling points

for members of all three for members of all three families increases with families increases with molecular weight due to the molecular weight due to the London dispersion interactions.London dispersion interactions.

• For a given molecular weight, For a given molecular weight, the alcohols and carboxylic the alcohols and carboxylic acids have a higher boiling acids have a higher boiling point than esters, this is point than esters, this is because they can form because they can form hydrogen bonds and esters hydrogen bonds and esters cannot.cannot.

• The carboxylic acids have a The carboxylic acids have a slightly higher boiling point slightly higher boiling point than alcohols, because they than alcohols, because they can form two hydrogen bonds can form two hydrogen bonds with a neighboring molecule (with a neighboring molecule (See Figure 4.23 in Raymond))

Molecular Weight {g/mol}Molecular Weight {g/mol}

Boili

ng P

oint

{°C

}Bo

iling

Poi

nt {

°C}

61


Another distinguishing characteristic of many of the families is Another distinguishing characteristic of many of the families is odor.odor.

• You nose is actually a highly sensitive chemical detector.You nose is actually a highly sensitive chemical detector.

• The members of different families can interact differently The members of different families can interact differently with the receptors in your nose to produce smells that are with the receptors in your nose to produce smells that are characteristic of the families they belong to.characteristic of the families they belong to.

• For example:For example:• Carboxylic acids produce the pungent, sometime unpleasant odors associated Carboxylic acids produce the pungent, sometime unpleasant odors associated

with ripe cheeses, rancid butter and vomit.with ripe cheeses, rancid butter and vomit.

• Esters, on the other hand, produce the sweet, often pleasant order associated Esters, on the other hand, produce the sweet, often pleasant order associated with flowers, perfumes and various natural and artificial flavorings. The next slide with flowers, perfumes and various natural and artificial flavorings. The next slide shows Figure 4.24 from Raymond, which gives some specific examples.shows Figure 4.24 from Raymond, which gives some specific examples.

62

Examples of some Examples of some flavorable esters:flavorable esters:


The EndThe End

Documents

Chem 150 Unit 2 - Hydrocarbons & Functional Groups