Theoretical description of the conformation and the tautomerism of progabide

A theoretical description of the conformation and tautomerism of the progabide molecule was performed employing the ab initio STO-3G and 3-21G basis sets and a quantum chemical reaction field model for the consideration of the solvent influence. The calculations indicated a conformation with planar orientation of the A ring and considerable rotation of the B ring with respect to the imine bond as the most stable conformation. The consequences for conformation of hydrogen bond formation and breaking were examined. Predominance of the aromatic tautomer in apolar and the quinonoid tautomer in polar solvents is predicted.