In this chapter, we will see many variations of a reaction type known as nucleophilic acyl substitution, the substrates for which are not aldehydes and ketones but carboxylic acid derivatives, such as...In this chapter, we will see many variations of a reaction type known as nucleophilic acyl substitution, the substrates for which are not aldehydes and ketones but carboxylic acid derivatives, such as acyl phosphates, thioesters, esters, and amides. As we shall soon see, these reactions are especially important in the metabolism of lipids (fats and oils) and in the formation and breakdown of peptide bonds in proteins.