OXYSULFUR COMPOUNDS DERIVED FROM DIMETHYL DISULFIDE - AN AB-INITIO STUDY

The optimized geometries of oxysulfur compounds derived from dimethyl disulfide were calculated at the MP2/6-31G level, and the relative en ergies of isomers in the CH3S2OCH3, CH3S2O2CH3, CH3S2O3CH3, and CH3S2O 4CH3 series were compared. All these derivatives are characterized by long S-S bonds or long sulfenyl or sulfinyl S-O bonds for sulfur-oxyge n-bridged isomers. According to the geometrical parameters calculated for vic-disulfoxide 4RR in the CH3S2O2CH3 series, this compound is bet ter described as two interacting sulfinyl radicals, and the obtained r esults substantiate the experimental scheme proposed by Clennan(28) fo r the intramolecular singlet oxygen addition on disulfides. The UV spe ctra of all these isomers were evaluated at a standard ab initio level : despite underestimated wavelengths, their evolution (wavelengths and molar extinction coefficients) is consistent with experiment and indi cates a strong influence of the sigma(S-S), n(S) --> sigma(S-S) trans ition for sulfur-sulfur-bridged isomers and of n(S),n(0) --> sigma(S-0 ) transitions for sulfur-oxygen-bridged isomers. As a result, these c ompounds will be cleaved photochemically by S-S or alternatively by su lfenyl or sulfinyl S-O bond cleavage, leading to oxysulfur radicals. T he numerous experimental data on oxysulfur molecules and radicals are discussed in light of the predicted stability and photochemical reacti vity of both classes of molecules. The validity of this standard metho d of evaluation of UV spectra was further assessed by a more accurate calculation on a known stable model compound, methyl methanethiosulfin ate (2), by use of an extensive configuration interaction treatment (M RSDCI formalism).