Synthesis and spectroscopic study of Schiff bases derived from trans-1,2-diaminocyclohexane. Deuterium isotope effect on 13C chemical shift

Abstract

The proton transfer in the intramolecular hydrogen bond in a series of Schiff bases derivatives of aromatic ortho-hydroxyaldehydes and trans-1,2-diaminocyclohexane has been studied by means of IR, UV–Vis, 1H and 13C NMR spectroscopies. The measurement of deuterium isotope effect on 13C chemical shift suggests that the proton transfer equilibria in both salicylidene moieties are not independent. Substitution of H by D in one hydrogen bond shifts the proton transfer equilibrium in one direction in this moiety, while in the opposite direction in the other.