SULFUR-COMPOUNDS .140. STRUCTURES AND RELATIVE STABILITIES OF 7 ISOMERIC FORMS OF H2S2O2

The ground-state geometries, energies, atomic charges and dipole moments of eight isomeric forms of H2S2O2 all containing an SS bond have been calculated at the HF/6-31G* level. The correlation energies have also been included up to the fourth order of Moeller-Plesset perturbation theory (MP4). The four most stable isomers are two rotamers of the chain-like HOSSOH (isomers 1 and 1a), and the thiosulphurous acids HOS(O)SH 2 and S = S(OH)2 3 the energies of which differ by less than 40.1 kJ mol-1. The four most stable structures have been refined at the HF/6-311G** level taking into account the correlation energy at level MP2 and zero-point energies, showing 2 to be the most stable isomer followed by 1 (symmetry C1), 1a (symmetry C2) and 3. The geometries obtained are compared to the known structures of organic derivatives. For isomers 1, 1a, 2 and 3 the wavenumbers of the 12 fundamental vibrations are given.