STRUCTURES, ENERGIES, AND VIBRATIONAL-SPECTRA OF SEVERAL ISOMERIC FORMS OF H2S2O AND ME(2)S(2)O - AN AB-INITIO STUDY

High-level ab initio MO calculations have been performed to determine the structures, energies, and vibrational spectra of eight isomers (in cluding rotamers) of H2S2O and five isomers/rotamers of Me(2)S(2)O. At the MP2/ 6-311G*//MP2/6-311G** level of theory, including the zero-p oint energies (ZPE), the order of decreasing stability of H2S2O molecu les is trans-HOSSH > cis-HOSSH > HOS(S)H > trans-HSS(O)H > cis-HSS(O)H > trans-HSOSH > cis-HSOSH > HS(O)(S)H. The remarkable stability of th e thiono derivative HOS(S)H over the sulfoxide HSS(O)H is explained by the stabilization of the former by an intramolecular OH...S hydrogen bond. The dimethyl derivatives of the more stable H2S2O isomers have b een calculated at the MP2/6-311G*//HF/6-311G**+ZPE level. The order o f decreasing stability is trans-MeOSSMe > cis-MeOSSMe > cis-MeSS(O)Me > trans-MeSS(O)Me > MeOS(S)Me. The geometrical parameters of these spe cies agree well with those of related compounds, e.g., MeOSSOMe and RS S(O)R with = p-tolyl.