Theoretical study of dimethyl maleate and its complexes with Lewis acids: Effect of the interaction between two methoxycarbonyl groups on equilibrium structures

The five equilibrium structures of dimethyl maleate were theoretically determined using the RHF and B3LYP methods. In all of the structures, one of the O=C-O planes is nearly perpendicular to, and the other is coplanar with, the C-C=C-C plane. It is well known that maleic acid diester has peculiar reactivity compared with other conjugated esters, which can be ascribed to the characteristics of the conformations. Calculations of complexes of dimethyl maleate and Lewis acids were performed, and the binding energies for the complexes were analyzed by decomposing them into the deformation energy and the interaction energy. For a comparison, the conformational properties of methyl acrylate and its Lewis acid complexes were also investigated.