The Characterization of the Electronic Spectra of Heterocyclic AmineN-Oxides by Means of the Non-Aqueous Oxidation and Reduction Potentials and the Substituent Effects on Them

The half-wave potentials of the voltammetric oxidation and the reduction of various heterocyclic amine N-oxides have been measured in CH3CN by the technique of a rotating platinum electrode. The reversibility of the electrode process was particularly examined for the oxidation reaction by analyzing the oxidation wave and by recording the ESR spectra. Then, the mutual relationship between the electronic spectra of these N-oxides and the values of the oxidation-reduction potentials was discussed in detail; we found that this kind of treatment is very useful in assigning the spectra. Finally, a good linear relation between the oxidation potentials of substituted pyridine N-oxides and the Hammett σ+ (Brown-Okamoto) constants was demonstrated and discussed.