Organic Chemistry

Penicillin G

T

he carbonyl group—a

carbon double bonded to

an oxygen—is probably the

most important functional group found

in organic compounds. Compounds containing

carbonyl groups— called carbonyl compounds—

are abundant in nature. Many play important roles in

biological processes. Hormones, vitamins, amino acids, drugs, and flavorings are just

a few of the carbonyl compounds that affect us daily. An acyl groupconsists of a car-

bonyl group attached to an alkyl group or to an aryl group.

The substituents attached to the acyl group strongly affect the reactivity of carbonyl

compounds. Carbonyl compounds can be divided into two classes. Class I carbonyl

compounds are those in which the acyl group is attached to an atom or a group that can

be replaced by another group. Carboxylic acids, acyl halides, acid anhydrides, esters,

and amides belong to this class. All of these compounds contain a group

or that can be replaced

by a nucleophile. Acyl halides, acid anhydrides, esters, and amides are all called

carboxylic acid derivativesbecause they differ from a carboxylic acid only in the na-

ture of the group that has replaced the OH group of the carboxylic acid.

OH

a carboxylic acid an acid anhydride

OR′ O R′

an ester

C

R

O

C

R

O

C

R

O

C

O

compounds with groups that can be replaced by a nucleophile

¬Cl,¬Br,¬O(CO)R,¬OR,¬NH 2 ,¬NHR, ¬NR 2 )

(¬OH,

a carbonyl group acyl groups

R

C

O

Ar

C

O

C

O

670

17

Carbonyl Compounds I

Nucleophilic Acyl Substitution

an acyl chloride

an ester

a carboxylic acid

an amide