Electron spin resonance and polarographic studies of the radical-anions of some nitrogen- and sulphur-containing heterocyclic molecules

Abstract

The electron spin resonance spectra of the radical-anions of 2,1,3-benzoxadiazole, 2,1,3-benzothiadiazole, 2,1,3-benzoselenadiazole, naphtho[2,3-c]-[1,2,5]thiadiazole, naphtho[1,2-c]-[1,2,5]thiadiazole, and naphtho[1,8-cd]-[1,2,6]thiadiazine are interpreted using molecular orbital theory. A p-orbital model gives a satisfactory description of the bonding of sulphur. The model also yields a reasonable correlation for the one-electron half-wave reduction potentials of the molecules. It is suggested that the interpretation of the hyperfine splittings in the electron spin resonance spectra of radicals containing conjugated sulphur is not a sufficient criterion for judging the relative merits of p- and d-orbital models.