A single-crystal ESR study on radicals derived from rac- and meso-1,2-dimethyl-1,2-diphenyldiphosphine disulfide: stereochemical selection in radical formation.

An ESR study on electron-capture phosphorus centered radicals trapped in single crystals of racand meso-1,2dimethyl-l,2-diphenyldiphosphine disulfide (MePhP(S)P(S)MePh) is reported. The principal values and axes of the g and hyperfine coupling tensors of the radical anions are determined. It is shown that X irradiation of the two diastereoisomeric compounds results in completely different radical products. The racemate yields a radical product in which the extra electron is symmetrically distributed over the two phosphorus nuclei, whereas for the meso form exclusively asymmetric electronic configurations are detected. For many years the formation and structure of free radicals, produced by ionizing radiation, has received much attention. Numerous ESR experiments have been performed to elucidate the principles that determine the electronic structure and molecular geometry of the formed doublet species. This has resulted in a detailed understanding of the role of the nucleus a t the radical center and of the influence of the surrounding ligands. Stereochemical aspects, however, are not generally included in these analyses. In the present study we report the formation of phosphorus-centered radicals in single crystals of racemic (R ,R and 0002-7863/88/1510-6001$01.50/0