STUDIES OF INTRAMOLECULAR HYDROGEN-BONDS IN DI-SCHIFF BASES OF 2-HYDROXY-5-METHYL ISOPHTHALDEHYDE

Di-Schiff bases obtained by the reaction of 2-hydroxy-5-methyl isophth aldehyde with 4-R-anilines (R = H, CH3 and OCH3) were synthesized and studied by ultraviolet-visible (UV-vis) spectrophotometry and H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy. The UV-vis spectra of di-Schiff bases 1-3 and their protonated and deprotonated analogue s in acetonitrile are discussed. Isotope effects on the C-13 NMR chemi cal shifts resulting from deuteration of the OH groups were determined . Inequivalence of the two 4-R-phenyl-imino methyl groups at low tempe ratures was evidenced. (C) 1998 Elsevier Science B.V.