AB-INITIO MCSCF STUDY OF THE HOMOLYTIC S-S BOND-DISSOCIATION IN DISULFIDES, THIOSULPHINATES AND ALPHA-DISULPHOXIDES

The geometrical and electronic properties of RSSR RS(O)SR and RS(O)S(O)R (with R=H,CH3) molecules and the energy profile for S-S bond cleavage were calculated with ab-initio MO MCSCF wavefunctions at 3-21G* level. The results show that the electronic structure of alpha-disulphoxides is more likely that of two paired radicals with net spin population localized on the oxygen atoms. Also in terms of bond-length and bond-index the S-S bond in alpha-disulphoxides appears to be much weaker than in the other molecules, as also confirmed by the calculated bond dissociation energy (DE) which turns out much lower than expected for a true SS bond.