ESR Study of Polyazine Anions

Abstract

Electron spin resonance measurements have been made on dimethyl sulfoxide solutions of the anion radicals of s‐tetrazine, pyridazine, phthalazine, and phenazine, as well as the diprotopyrazine cation radical. The radicals were generated by constant potential electroreduction of the parent compound at a mercury pool cathode within the microwave cavity. Complete assignment of the hyperfine coupling constants to positions of phthalazine anion was made by selective deuteration and the help of a spectral synthesis program. Satellites due to the C¹³ hyperfine interaction of pyrazine anion have been observed, and the coupling constant measured. The mechanism of N¹⁴ hyperfine interactions in polyazine anion radicals is discussed in terms of earlier theories of C¹³ interaction. We find that π‐electron spin density on nearest‐neighbor N atoms affects a_N strongly, whereas on nearest‐neighbor C atoms it does not. Values for several empirically determined spin‐polarization parameters are reported.