Crystal structure and geometry-optimization study of 2-benzyliminiomethylene-4-nitrophenolate

Abstract

5-Nitro-2-hydroxybenzaldehyde condenses with benzylamine to yield a Schiff base that exists in the solid state as zwitterionic form as 2-benzyliminiomethylene-4-nitrophenolate. In the crystal structure, two zwitterions are linked together as a centrosymmetric dimer by hydrogen bonds involving the iminium hydrogen atom [N···O_intramonomer=2.653(2), N···O_intradimer=2.880(2) Å]. Geometry-optimizations on the monomeric zwitterion and the isomeric hypothetical 2-benzyliminomethylene-4-nitrophenol molecule by the B3LYP/6-31++G(d,p) method imply an endothermic process [ΔH=12.4 kcal mol^-1] for the transfer of the phenolic proton in the hypothetical neutral molecule to furnish the zwitterionic molecule.