Crystal structure and DFT study of the zwitterionic form of 3-{(E)-1-[(4-ethoxyphenyl)iminiumyl]ethyl}-6-methyl-2-oxo-2H-pyran-4-olate

Abstract

The title Schiff base compound, C16H17NO4, crystallizes as a zwitterion, with the phenolic H atom having been transferred to the imino group. The resulting iminium and hydroxy groups are linked by an intramolecular N—H...O hydrogen bond, enclosing an S(6) ring motif. The conformation about the C=N bond is E and the dihedral angle between the benzene and pyran rings is 70.49 (6)°. In the crystal, molecules are linked by C—H...O hydrogen bonds, forming a three-dimensional supramolecular structure. There are also C—H...π interactions and offset π–π interactions, involving the pyran rings [intercentroid distance = 3.4156 (8) Å], which consolidate the three-dimensional structure. Quantum chemical calculations of the molecule are in good agreement with the solid state keto–amine (NH) form of the title compound.