Electron spin resonance spectroscopy, stability and spin-probe properties of dithiazolyl, dithiadiazolyl, benzodithiazolyl and disulphenimidyl free radicals

A comparative investigation has been made of the e.s.r. spectra of 1,3,2-dithiazol-2-yl, 1,3,2,4-dithiadiazol-2-yl, 1,3,2-benzodithiazol-2-yl and dibenzenesulphenimidyl free radicals, both in solution and in rigid matrices. The powder spectra were analysed to give values for the anisotropic g-factors and hyperfine coupling constants, and, in turn, these results were used by means of a simple e.s.r. tumbling theory to calculate radical radii from low-temperature fluid e.s.r. spectra. A simple correction was incorporated into the theory to include a contribution from ‘slip’ rotation. The values of the nitrogen isotropic coupling constants provide a useful guide to the electronic and spatial structures of the radicals. It is shown that the 1,3,2-dithiazol-2-yl radicals have the greatest potential as spin probes.