TAUTOMERISM IN 2-HYDROXY-L-NAPHTHALDEHYDE SCHIFF-BASES IN SOLUTION AND THE SOLID-STATE INVESTIGATED USING C-13 NMR-SPECTROSCOPY

C-13 and H-1 NMR spectra of six Schiff bases formed from 2-hydroxy-1-naphthaldehyde and substituted anilines were measured and assigned in a variety of solvents. Based on the C-13 chemical shifts and (3)J(CH,NH), the ratio of the keto-amine and phenol-imine tautomers was derived using both C-13 chemical shifts and H-1-H-1 coupling constants, the two methods giving comparable results. The solid-state C-13 NMR spectra of two of these Schiff bases were also measured and interpreted. Based on chemical shift assignments from solution NMR, which showed a relationship between certain shifts and the proportions of the tautomers, it has been shown that these compounds exist essentially as the keto-amine form in the solid, the tautomer previously shown to be the more thermodynamically stable.