John McMurry, Professor Emeritus

21.1 • Naming Carboxylic Acid Derivatives

Acid Halides, RCOX

Acid halides are named by identifying first the acyl group and then the halide. As described in Section 20.1 and shown in Table 20.1, the acyl group name is derived from the carboxylic acid name by replacing the -ic acid or -oic acid ending with -oyl, or the -carboxylic acid ending with -carbonyl. To keep things interesting, however, IUPAC recognizes eight exceptions for which a -yl rather than an -oyl ending is used: formic (formyl), acetic (acetyl), propionic (propionyl), butyric (butyryl), oxalic (oxalyl), malonic (malonyl), succinic (succinyl), and glutaric (glutaryl).

The structures of three acid halides. The first is acetyl chloride, the second is benzoyl bromide, and the third is cyclohexanecarbonyl chloride.

Acid Anhydrides, RCO₂COR′

Symmetrical anhydrides of unsubstituted monocarboxylic acids and cyclic anhydrides of dicarboxylic acids are named by replacing the word acid with anhydride.

The structures of three acid anhydrides. The first is acetic anhydride, the second is benzoic anhydride, and the third is succinic anhydride.

Unsymmetrical anhydrides—those prepared from two different carboxylic acids—are named by listing the two acids alphabetically and then adding anhydride.

The structure of acetic benzoic anhydride which comprises of two carbonyl groups linked by an oxygen atom. A methyl group is attached to one of the carbonyls and a benzene ring to the other.

Esters, RCO₂R′

Esters are named by first identifying the alkyl group attached to oxygen and then the carboxylic acid, with the -ic acid ending replaced by -ate.

The structures of three esters. The first is ethyl acetate, the second is dimethyl malonate, and the third is tert-butyl cyclohexane carboxylate.

Amides, RCONH₂

Amides with an unsubstituted –NH₂ group are named by replacing the -oic acid or -ic acid ending with -amide, or by replacing the -carboxylic acid ending with -carboxamide.

The structures of three amides. The first is acetamide, the second is hexanamide, and the third is cyclopentane carboxamide.

If the nitrogen atom is further substituted, the compound is named by first identifying the substituent groups and then the parent amide. The substituents are preceded by the letter N to identify them as being directly attached to nitrogen.

The structures of a secondary and a tertiary amide. The first structure is N-methylpropanamide and the second is N, N-diethylcyclohexanecarboxamide.

Thioesters, RCOSR′

Thioesters are named like the corresponding esters. If the related ester has a common name, the prefix thio- is added to the name of the carboxylate: acetate becomes thioacetate, for instance. If the related ester has a systematic name, the -oate or -carboxylate ending is replaced by -thioate or -carbothioate: butanoate becomes butanethioate and cyclohexanecarboxylate becomes cyclohexanecarbothioate, for instance.

The structures of three thioesters. The first is methyl thioacetate, the second is ethyl butanethioate, and the third is methyl cyclohexanecarbothioate.

Acyl Phosphates, RCO₂PO₃^2– and RCO₂PO₃R′^–

Acyl phosphates are named by citing the acyl group and adding the word phosphate. If an alkyl group is attached to one of the phosphate oxygens, it is identified after the name of the acyl group. In biological chemistry, acyl adenosyl phosphates are particularly common.

The structures of two acyl phosphates. The first is benzoyl phosphate and the second structure is acetyl adenosyl phosphate.

A summary of nomenclature rules for carboxylic acid derivatives is given in Table 21.1.

Table 21.1 Nomenclature of Carboxylic Acid Derivatives

Functional group	Structure	Name ending
Carboxylic acid		-ic acid (-carboxylic acid)
Acid halide		-oyl halide (-carbonyl halide)
Acid anhydride		anhydride
Amide		-amide (-carboxamide)
Ester		-oate (-carboxylate)
Thioester		-thioate (-carbothioate)
Acyl phosphate		-oyl phosphate