NMR spectroscopy of 2-hydroxy-1-naphthylidene Schiff bases with chloro and hydroxy substituted aniline moiety

Schiff bases, products of the reaction of primary amines and carbonyl compounds, are involved in many metabolic processes. Hence, physicochemical studies of Schiff bases as model substances can contribute to a better understanding of biological systems. In this work, the oneand two-dimensional homo- and heteronuclear 1H and 13C NMR spectra of 2-hydroxy-1-naphthylidene Schiff bases with differently chloro- and hydroxyl- substituted aniline moiety were studied. The spectra were analyzed on the basis of chemical shifts, substituent effects, spinspin couplings as well as connectivities. It was established that the investigated Schiff bases exist as NH tautomers in DMSO-d6 solution with NH group orientated in cis position relative to the carbonyl of naphthylidene moiety. The positions of substituents on aniline ring were found to be in agreement with intra- and intermolecular hydrogen bond formation. Influence of substituents on planar or nonplanar conformation of compounds is discussed as well