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

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) A], 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.