CONFORMATIONAL STUDIES OF THIYL AND SELENENYL RADICALS

Muonium adds to the unsaturated bond in 1,3-dithiolane-2-thione or -2- selenone to form a chalcogen-centered radical. The muon hyperfine coup ling constants (hfc) were measured for both compounds over a range of temperatures. In solution, the temperature dependence of the muon hfc indicates that for the thiyl radical the preferred conformation corres ponds to the muon eclipsing the unpaired electron p(z)-orbital, while there is practically free rotation in the case of the selenenyl radica l in the temperature range studied. In pure thione the hfc values show a remarkable discontinuity at the melting point. The two radical sign als seen in the solid are interpreted as due to the presence of two do minant crystal orientations in the samples studied. In pure selenone d ata were obtained only in the solid. For both systems, the solid phase results show that interaction between the muon and the unpaired elect ron spin is enhanced compared to the liquid phase and/or the solution.