Theoretical investigations of the protonation of dihydrogen sulphoxide and intramolecular interconversion of the protonated sulphoxide and hydrogen thioperoxide

Abstract

Protonation on dihydrogen sulphoxide (H₂SO) and intramolecular interconversion of H₂S⁺OH and HSOH have been examined by means of ab initio MO calculations with STO–3G and 4–31 G basis sets. The results imply that H₂SO forms a more striking pyramidal conformation upon protonation, and that the trans-staggered form of H₂S⁺OH is more stable than the cis-staggered one. The difference can be correlated with the change of the polarization of the S–O bond and/or the π-electron density on the SO fragment. The intramolecular interconversion of H₂S⁺OH proceeds via pseudo-rotation but not via oxygen inversion or sulphur-pyramidal inversion. This behaviour is quite different from that of protonated carbonyl compounds. The intramolecular interconversion of hydrogen thioperoxide (HSOH) is also predicted to proceed via the transition state of the trans-conformation on the rotational path with lower energy barrier than the case of H₂S⁺OH. The relative stability of the transition states for interconversion is also discussed in connection with the changes in some particular MO energy levels.