Carboxylic acids:

Where carboxylic acids fit into the reactivity order do explained above? The nucleophilic substitution of carboxylic acids is complicated from the fact that an acidic proton is exists. Because most nucleophiles can work as bases, the reaction of a carboxylic acid along with a nucleophile results in an acid-base reaction than nucleophilic substitution.

Though, carboxylic acids can go through nucleophilic substitution if they are activated in advance.