A carboxylic acid derivative is a compound related to a carboxylic acid by replacing the hydroxyl (–OH) of the carboxyl group with another group. It matters because all such derivatives share the same characteristic reaction, nucleophilic acyl substitution, and can be interconverted. The class includes acyl chlorides, acid anhydrides, esters and amides, which differ markedly in reactivity according to how good a leaving group the replacing group provides.

羧酸衍生物是通过把羧基中的羟基(–OH)换为其他基团而与羧酸相关的化合物。它之所以重要,是因为所有这类衍生物都具有相同的特征反应——亲核酰基取代,并可相互转化。该类包括酰氯、酸酐、酯和酰胺,它们的反应性因所替换基团作为离去基团的优劣不同而差别显著。