Provide an example of the nucleophilic substitution of different carboxylic acids.

Nucleophilic substitution is a reaction in which a nucleophile replaces a leaving group from a molecule. Carboxylic acids can undergo nucleophilic substitution reactions, such as esterification and amidation.

In esterification, a carboxylic acid reacts with an alcohol in the presence of an acid catalyst to form an ester and water. The nucleophile is the alcohol, which attacks the carbonyl carbon of the carboxylic acid, displacing the leaving group (a protonated water molecule). This reaction is reversible, and the equilibrium can be shifted towards the product by removing water from the reaction mixture.

In amidation, a carboxylic acid reacts with an amine in the presence of a coupling agent (such as DCC) to form an amide and a molecule of water. The nucleophile is the amine, which attacks the carbonyl carbon of the carboxylic acid, displacing the leaving group (a protonated amine molecule). This reaction is also reversible, and the equilibrium can be shifted towards the product by using an excess of the amine or by removing water from the reaction mixture.

Overall, nucleophilic substitution reactions of carboxylic acids are important in organic synthesis, as they allow the formation of esters and amides, which are widely used in the production of pharmaceuticals, fragrances, and polymers.