Tautomerism of 2-hydroxynaphthaldehyde Schiff bases

A UV-Vis spectroscopic study based on the recently developed chemometric ap proach for quantitative analysis of undefined mixtures is performed on a se ries of donor and acceptor substituted Schiff bases of 2-hydroxynaphthaldeh ydes. In CCl4 solution all compounds preferentially exist as the phenol tau tomer independent of the nature of the respective substituent. With increas ing polarity the tautomeric equilibrium is shifted towards the quinone form . In CHCl3 and, especially, ethanol a clear distinction between the effect of donors (stabilization of the quinone form) and acceptors (stabilization of the phenol tautomer) is evident. Ab initio calculations including solven t effects via the polarized continuum model of solvation as well as the sup ermolecule approach are used to rationalize the experimental findings.