The Effect of Intramolecular Hydrogen Bonding on the Polarographic Reduction Potentials of Azomethines

Abstract

Abstract The effects of intramolecular hydrogen bonding on the polarographic reduction potentials (E1⁄2) of several azomethines, such as N-salicylidenemethylamine, N,N′-bis(salicylidene)ethylenediamine, N-salicylideneaniline, N-salicylidene-o-aminophenol, and N-benzylidene-o-amino-p-substituted phenols, have been studied in aqueous and non-aqueous solutions. Contrary to expectations, a larger negative shift of E1⁄2 was observed in the case of o-OH-substituted azomethines than in that of unsubstituted azomethines in buffer solutions. On the other hand, the E1⁄2 of the substituted compounds shifted 0.3–0.4V toward the positive side in dimethylformamide or acetonitrile. The relative strengths of hydrogen bonds, as estimated from the positive shifts of E1⁄2, were 6–10 kcal/mol. It has been proposed, from the hydrogen bond strength, the UV spectra, and the p-substituent effects, that the introduction of an o-OH group into the phenylimino ring provides not a periperpendicular conformation, but a coplanar configuration, by means of the formation of the O–H···N hydrogen bond.