Intramolecular cation exchange in ion pairs. Part II. Isomeric radical ion pairs of dithiolactones

The radical ion pairs of several dithiolactones have been studied by e.s.r. spectroscopy. The e.s.r. spectral shape is strongly temperature dependent owing to the intramolecular migration of the alkali counterion between the two carbonyl groups of the organic anion. In the case of asymmetric derivatives, two non-equivalent ion pairs have been unambiguously detected for the first time. The factors affecting their relative stability are described. The kinetics of the cation exchange has been investigated for some of the compounds examined, by analysing the line shape variations with temperature. It is emphasized that the activation parameters calculated on the usual assumption that the change of temperature influences only the rate of migration should be considered with some caution since parallel changes of the structure of the ion pairs may also occur. The effects of these variations on the measured parameters are discussed.