Nomenclature of Carboxylic Acid Derivatives: Acid Halides, Esters, and Acid Anhydrides

Acid halide names derive from parent carboxylic acids by replacing the suffix "-ic acid" with "-yl halide." For example, ethanoic acid becomes ethanoyl chloride in IUPAC nomenclature, while acetic acid becomes acetyl chloride in common nomenclature. For cyclic acid halides, the suffix "-carboxylic acid" changes to "-carbonyl halide."

Esters are named by citing the alkyl group attached to oxygen first, then the acid name with "-ic acid" replaced by "-ate." Cyclic esters, called lactones, use "-olactone" instead. Ring size is indicated by a number in IUPAC names or a Greek letter in common names, such as γ-butyrolactone for the common name.

Symmetrical anhydrides form from two identical carboxylic acids and are named by replacing "-acid" with "-anhydride," such as acetic anhydride. Unsymmetrical anhydrides form from two different acids and list both acid names alphabetically before adding "-anhydride," for example, acetic propionic anhydride.

Cyclic anhydrides derived from dicarboxylic acids follow the same naming rules as acyclic anhydrides. The suffix "-acid" is replaced with "-anhydride." For instance, butanedioic acid becomes butanedioic anhydride in IUPAC nomenclature, while succinic acid becomes succinic anhydride in common nomenclature.

Numbering identifies the oxygen atom's position on the lactone ring. In IUPAC names, carbons are numbered starting from the carbonyl carbon, and this number is added as a prefix, such as 4-butanolactone. In common names, a Greek letter replaces the number, with the carbon adjacent to the carbonyl carbon labeled first.

The parent carboxylic acid name directly determines the acid halide name through systematic suffix replacement. Both IUPAC and common names follow this pattern: the acid's base name is retained, and only the acid suffix changes to the halide suffix. This approach ensures consistency and clarity in nomenclature of carboxylic acid derivatives.

The alkyl group bonded to the oxygen atom is named first in ester nomenclature, followed by the carboxylic acid name with its suffix modified. For example, methyl ethanoate has methyl as the alkyl group and ethanoate as the acid portion, derived from ethanoic acid.