Chap 18 Carboxylic acids and their derivatives. nucleophilic substitution at the acyl carbon 18.1 Introduction The carboxyl group,-COOH,-CO2H, is one of the most widely occurring functional groups in chemistry and biochemistry. Not only are carboxylic acids themselves important, but the carboxyl group is the parent group of a large family of related compoundsChap 18. Carboxylic acids and their derivatives. Nucleophilic substitution at the acyl carbon 18.1 Introduction The carboxyl group, -COOH, -CO2H, is one of the most widely occurring functional groups in chemistry and biochemistry. Not only are carboxylic acids themselves important, but the carboxyl group is the parent group of a large family of related compounds