Nucleophilic acyl substitution is the characteristic reaction of carboxylic acid derivatives. A nucleophile adds to the electron-deficient carbonyl carbon to give a tetrahedral intermediate; this intermediate then collapses, expelling the leaving group and re-forming the carbonyl group (C=O). It matters because it is the means by which one acid derivative is converted into another. It is distinguished from nucleophilic addition to a carbonyl by this final step in which a leaving group is expelled.

亲核酰基取代是羧酸衍生物的特征反应。亲核试剂加到缺电子的羰基碳上,生成一个四面体中间体;该中间体随后塌缩,排出离去基团并重新形成羰基(C=O)。它之所以重要,是因为它是把一种酸衍生物转化为另一种酸衍生物的途径。它与对羰基的亲核加成相区别,区别就在于这一排出离去基团的最后步骤。