Electron spin resonance spectra observed in dilute solutions of the hexafluoroarsenate salts of selenothiadiazolylium cations in polar solvents are ascribed to the parent cation radicals [Formula: see text], [Formula: see text], [Formula: see text], and[Formula: see text]. The g- and nitrogen hyperfine tensors for the three selenium-containing species are entirely in line with the planar π-radical description deduced in earlier studies of trithiadiazolylium. Substantial increases in the g-shifts on substitution of sulphur by selenium result in broadening of the solution spectra and concomitant loss of nitrogen hyperfine structure. From measurements made in solid SO2, the following principal tensor components were deduced for the new, Se-containing radicals:[Formula: see text]: g = (1.9930, 2.0108, 2.1379), aN(2) = (7.4, ≈0, ≈0) gauss, aSe(2) = (180, 70, 43) gauss;[Formula: see text]: g = (1.9941, 2.0108, 2.1355), aN(2) = (6.9, ≈0, ≈0) gauss, aSe(2) = (180, 70, 45) gauss;[Formula: see text]: g = (1.9957, 2.0086, 2.0736), aN(2) = (8.3, ≈0, ≈0) gauss, aSe = (198, 78, 75) gauss, where the values are given in the order x, y, z, x being the direction perpendicular to the radical plane.
An electron spin resonance study of cholestane spin label in aqueous mixtures of biliary lipids