The electron-spin resonance spectra of the electrolytically generated radical-anions of the nitrothiophens

Abstract

The radical-anions of 2-nitro-, 3-nitro-, and 2,5-dinitro-thiophen have been generated by electrolysis of their solutions in both acetonitrile and dimethylformamide, and their electron-spin resonance spectra measured. The proton hyperfine splitting constants have been assigned by observation of the spectra of various methylated derivatives. Spin-densities have been calculated by McLachlan's extension of the Hückel molecular orbital method, using models for the sulphur atom in which either only the occupied 3p_z orbital interacts with the π-system (p-model) or where the vacant 3d orbitals are also taken into account (d-model). Both models give fairly adequate predictions of the experimental results. A suitable set of parameters to describe the sulphur atom in the p-model for both these compounds and the radical-anions of dibenzothiophen and its derivatives is α_S=α+ 1·0β, β_CS= 0·7β, where α and β have their usual significance.