The chemistry leading to the competitive eliminations of H, CH3, and OCOCH3 from adducts of ionized methyl benzoate and neutral methyl isocyanide has been explored using density functional theory molecular orbital calculations. The energies of the various reactants and transition structures were estimated at the B3LYP/6-31 +G(d,p) level of theory. Nucleophilic aromatic substitution is proposed to account for the H and OCOCH3 eliminations. The corresponding sigma-complex intermediates, B-lipso and B-lortho, are stable species lying in deep energy wells Situated 70 and 120 kJ/mol, respectively, below the reactants, ionized methyl benzoate and methyl isocyanide. The latter complex, B-lortho, may be also at the origin of a multistep rearrangement involving hydrogen migrations and methyl elimination from the original methoxy group of the benzoate moiety.