STRUCTURES, ENERGIES, TORSIONAL BARRIERS, AND VIBRATIONAL-SPECTRA OF 3 ROTAMERS OF TETRASULFANE, H2S4

Ab initio calculations at the MP2/6-311 G(*)//MP2/6-311 G(**) level s how that the all-trans, cis-hans and all-cis rotamers of H2S4 are prac tically of identical energy. Their vibrational wavenumbers are also pr actically identical and in agreement with the observed infrared and Ra man spectra of dissolved H2S4. On rotation about the central bond of H 2S4 the torsional barriers are found to be 32.0 (cis-barrier) and 26.6 kJ mol(-1) (trans-barrier). The geometries of the two transition stat es with tau(SSSS) = 0 degrees and 180 degrees can be explained by hype rconjugation between the lone pairs at the terminal sulfur atoms and t he sigma() molecular orbital of the central bond.