Nucleophilic acyl substitution is a fundamental reaction in organic chemistry where a nucleophile attacks a carbonyl carbon of a carboxylic acid derivative, leading to the replacement of a leaving group with the nucleophile. This process is crucial for forming various functional groups, as it allows for the transformation of carboxylic acid derivatives into other compounds such as esters and amides. The stability of the carbonyl compound and the nature of the leaving group significantly influence the reaction's efficiency and outcome.