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Abstract
Infrared, 1H-NMR and UV-visible spectra of a series of substituted 2-hydroxy-1-naphthaldehyde Schiff bases were used to investigate enol-imine and keto-amine tautomeric equilibrium. They were synthesised and studied by elemental analysis. From the IR spectra of the model compounds it was possible to assign the IR absorption for the C═O and the C═N groups in both the keto-amine and enol-imine forms. It was possible to assign other absorptions which were either specific to the keto-amine or the enol-imine forms. Specific pattern was observed for all the studied compounds. The UV-visible spectra of compounds have been investigated in different solvent, acidic and basic media. The compounds were in tautomeric equilibrium (enol-imine O─H ⃛N, keto-amine O ⃛H─N forms) in polar and non-polar solvents. The keto-amine form was observed in basic solutions of DMSO, ethanol, chloroform, benzene, cyclohexane and in acidic solutions of chloroform and benzene, but not in acidic solutions of DMSO and ethanol.