Abstract <p>The reactions of acyl chlorides with carboxylic acids were studied by the B3LYP/aug-cc-pVDZ method at a temperature of 298 K. It is shown that the mechanism and activation barriers are determined by the formation of hydrogen-bonded complexes with various substituents. It was established that in a neutral medium, trichloroacetyl chloride acts as an efficient activating agent, forming a mixed anhydride. Reactions of benzoyl chloride with aliphatic and aromatic carboxylic acids are limited to the direct reaction. In contrast, trichloroacetyl chloride can lead to the formation of anhydride only via an intermediate. The feasibility of these reactions is determined by the competition between the activation barriers and thermodynamic resolution, which are controlled by the nature of substituents in the reagents. The majority of the reactions under study are reversible and kinetically feasible under normal conditions or at elevated temperatures. If the reagents are thermodynamically favorable, the equilibrium can be shifted toward the reaction products by removing HCl from the system.</p>