Reactions of carboxylic acids and carboxylic acid derivatives figure prominently on the new MCAT because they figure prominently in biochemistry. From the mechanism of a serine protease to triglyceride synthesis, acyl substitution is omnipresent in biochemistry. Acyl substitution is reaction pathway for transforming one carboxylic acid derivative into another, moving between carboxylic acids, amides, esters, anhydrides, thioesters and acyl phosphates. Other carboxylic acid reactions important in biochemistry include Claisen condensation, alpha addition, and formation and use of a carboxylate nucleophile. Additionally, the way that thiamine pyrophosphate (TPP) assists decarboxylation of an α-keto acid in pyruvate dehydrogenase and α-ketoglutarate dehydrogenase is very similar to the benchtop decarboxylation of a β-keto acid.
nucleophilic acyl substitution mechanism

Nucleophilic acyl substitution mechanism.