Chapter 21

Copyright © 2010 Pearson Education, Inc.

Organic Chemistry, 7th EditionL. G. Wade, Jr.

Part 1: Structure and Properties of Carboxylic Acid Derivatives

Chapter 21 2

Acid Derivatives

All the derivatives can be converted to the carboxylic acid by acidic or basic hydrolysis.

Esters and amides are commonly found in nature.

Chapter 21 3

Esters from Carboxylic Acids

Esters can be made from the carboxylic acid through the Fischer esterification.

Excess alcohol is used to drive the equilibrium toward the ester.

Chapter 21 4

Nomenclature of Esters

Esters are named as alkyl carboxylates. The first word is derived from the alkyl group

of the alcohol, and the second word from the carboxylate group of the carboxylic acid.

Chapter 21 5

Cyclic Esters

Reaction of —OH and —COOH on same molecule produces a cyclic ester called lactone.

To name, add the word lactone to the IUPAC acid name or replace the -ic acid of common name with -olactone.

Chapter 21 6

Amide Structure

Amides are the product of the reaction of a carboxylic acid with ammonia or an amine.

Not basic because the lone pair on nitrogen is delocalized by resonance.

The C—N bond has double-bond character.

Chapter 21 7

Protonation of Amides

Under acidic conditions, the double-bonded oxygen will get protonated.

Chapter 21 8

Classes of Amides

1 amide has one C—N bond (two N—H). 2 amide or N-substituted amide has two C—N bonds

(one N—H). 3 amide or N,N-disubstituted amide has three C—N

bonds (no N—H).

3º amide 2º amide 1º amide

Chapter 21 9

Nomenclature of Amides

For 1 amide, drop -ic or -oic acid from the carboxylic acid name, add -amide.

Alkyl groups bonded to nitrogen are named with N-alkyl to indicate their attachment to the nitrogen atom.

N-ethyl-N-methyl-2-dimethylpropanamide(N-ethyl-N-methylisobutyramide)CH3CHC N

O

CH2CH3

CH3

CH3

Chapter 21 10

Cyclic Amides

Cyclic amides are called lactams. To name, add the word lactam to the IUPAC

acid name or replace the -ic acid of common name with -olactam.

Chapter 21 11

Nitriles

Nitriles contain the cyano group (—CN). They can be hydrolyzed to carboxylic acids.

Chapter 21 12

Structures of Acetonitrile and Propyne

In both compounds, the atoms at the ends of the triple bonds are sp hybridized, and the bond angles are 180°.

In place of the acetylenic hydrogen atom, the nitrile has a lone pair of electrons in the sp orbital of nitrogen.

The nonbonding electrons on the nitrogen are not basic.

Chapter 21 13

Naming Nitriles

For IUPAC names, add -nitrile to the alkane name. The Ethyl Octanoate group can also be named as a

substituent, the cyano group. Common names come from the carboxylic acid.

Replace -ic acid with -onitrile.

CH3 C N

acetonitrile 3-cyanopentanoic acid

CH3 CH2 CH CH2 COOH

CN

CN

cyclopropanecarbonitrile

Chapter 21 14

Acid Halides

R C Cl

O

R C Br

O

acid chloride(acyl chloride)

acid bromide(acyl bromide)

Also called acyl halides. These are more reactive than carboxylic acids, so

they are used to synthesize other acid derivatives such as esters and amides.

Used in the Friedel–Crafts acylation to make acylbenzenes.

Chapter 21 15

Acid Halide Nomenclature

CH3CH2 C Cl

O

CH3CHCH2 C Br

OBr

propanoyl chloride 3-bromobutanoyl bromide

Named by replacing -ic acid with -yl halide. Acyl chlorides are more common.

Chapter 21 16

Acid Anhydrides

Two molecules of acid combine with the loss of water to form the anhydride.

Anhydrides are more reactive than acids, but less reactive than acid chlorides.

A carboxylate ion is the leaving group in nucleophilic acyl substitution reactions.

Chapter 21 17

Anhydride Nomenclature

CH3 C O

O

C

O

CH3 CF3 C O

O

C

O

CF3 CH3 C O

O

C

O

H

ethanoic anhydride(acetic anhydride)

trifluoroethanoic anhydride(trifluoroacetic anhydride)

ethanoic methanoic anhydride(acetic formic anhydride)

The word acid is replaced with anhydride. For a mixed anhydride, name both acids.

Chapter 21 18

Multifunctional Compounds The functional group with the highest priority

determines the parent name.

CH C NCH2CH3

OH

2-hydroxybutanenitrile

acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > alkyne

Chapter 21 19

Boiling Points of Carboxylic Acid Derivatives

Chapter 21 20

Intermolecular Forces of Amides

Chapter 21 21

Melting Points

Amides have very high boiling points and melting points compared to other compounds of similar weight.

Melting points increase with increasing number of N—H bonds.

Tertiary amides cannot hydrogen bond, but still have high boiling points.

Chapter 21 22

Solubility Acid chlorides and anhydrides are too

reactive to be used with water or alcohol. Esters, 3 amides, and nitriles are good

polar aprotic solvents. Solvents commonly used in organic

reactions: Ethyl acetate Dimethylformamide (DMF) Acetonitrile

Common Solvents

Chapter 21 23

Chapter 21 24

IR Spectroscopy

Chapter 21 25

IR Spectrum of Ethyl Octanoate

Chapter 21 26

IR Frequencies of Lactones and Lactams

• Ring strain in lactones and lactams increases the carbonyl stretching frequency.

Chapter 21 27

IR Spectrum of Propionic Anhydride

Chapter 21 28

Typical 1H–NMR Absorptions

Chapter 21 29

NMR Spectra of DMF

Chapter 21 30

13C–NMR Spectroscopy

The carbonyl carbons of acid derivatives appear at shifts around 170 to 180 ppm, slightly more shielded than the carbonyl carbons of ketones and aldehydes.

The -carbon atoms absorb around 30 to 40 ppm.