Organic Chemistry

678 CHAPTER 17 Carbonyl Compounds I

The boiling points of the ester, acyl chloride, ketone, and aldehyde are lower than the

boiling point of the alcohol with a comparable molecular weight because the mole-

cules of those carbonyl compounds are unable to form hydrogen bonds with each

other. The boiling points of the carbonyl compounds are higher than the boiling point

of the ether because of the polar carbonyl group.

Carboxylic acids have relatively high boiling points because they form intermolecular

hydrogen bonds, giving them larger effective molecular weights.

Amides have the highest boiling points, because they have strong dipole–dipole inter-

actions since the resonance contributor with separated charges contributes signifi-

cantly to the overall structure of the compound (Section 17.2). If the nitrogen of an

amide is bonded to a hydrogen, hydrogen bonds will form between the molecules. The

boiling point of a nitrile is similar to that of an alcohol because a nitrile has strong

dipole–dipole interactions (Section 2.9).

Carboxylic acid derivatives are soluble in solvents such as ethers, chlorinated alkanes,

and aromatic hydrocarbons. Like alcohols and ethers, carbonyl compounds with fewer

than four carbons are soluble in water.

Esters,N,N-disubstituted amides, and nitriles are often used as solvents because

they are polar, but do not have reactive hydroxyl or amino groups. We have seen that

dimethylformamide (DMF) is a common aprotic polar solvent (Section 10.3).

17.4 Naturally Occurring Carboxylic Acids

and Carboxylic Acid Derivatives

Acyl halides and acid anhydrides are much more reactive than carboxylic acids and

esters, which, in turn, are more reactive than amides. We will see the reason for this

difference in reactivity in Section 17.5.

Because of their high reactivity, acyl halides and acid anhydrides are not found in

nature. Carboxylic acids, on the other hand, are less reactive and arefound widely in na-

ture. For example, glucose is metabolized to pyruvic acid. (S)-(+)-Lactic acid is the

C CR

OHO

OH O

R

intermolecular

hydrogen bonds

bp = 97.4 °C

CH 3 CH 2 CH 2 OH

bp = 57.5 °C bp = 51 °C bp = 56 °C bp = 49 °C

bp = 10.8 °C

CH 3 CH 2 OCH 3

bp = 213 °C bp = 141 °C bp = 97 °C

CH 3 CH 2 CN

O

C

CH 3 Cl

O

C

CH 3 CH 3

O

C

CH 3 CH 2 H

O

C

CH 3 CH 2 OH

O

C

CH 3 CH 2 NH 2

O

C

CH 3 OCH 3

CN

CN

CN

NC

−

+

O

O−

R

R

+

R

R R

O−

+

H

R R

−O

+

R

RH

R

dipole–dipole

interactions

intermolecular

hydrogen bond

NCR

R CN

dipole–dipole

interactions

δ− δ+

δ+ δ−