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

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.

Voltammetric studies of the electrochemical behaviour of salicylidene-2-aminopyridine at a hanging-mercury-drop-electrode

“…Fresh where 5 = ( E -@ )~F / R T , a is the symmetry factor, Il and I 2 are the stock solution of the Schiff base (10 mM) was prepared from a fresh convolution currents given in eqS. [3] and [4], respectively, Ilim is the electrolyte solution on the same day that measurements were carried limit of 11 and E approaches infinity and i, is the exchange current for nut.…”

“…The measurements were done using a three i (~) d u [3] I; = I,(t) = 5,-l I 2 -electrode cell. It consists of a hanging mercury electrode with surface ,,(t -u)?…”

“…[3] and [4]. Figure 1 illustrates convoluted currents I, and l2 cyclic voltammograms for the first wave of 1.19 X lop3 M solution.…”