A quantum chemical study on the relative thermodynamic stabilities of the two isomeric species of C2H3S+

Abstract

Non-empirical SCF-MO wave functions were computed for the two limiting structures of C₂H₃S⁺ with full geometry optimization using three different atomic orbital bases. It was found that the bridged structure (thiirenium ion) was somewhat more stable (1–14 kcal mol^–1 depending on the basis set) than the open structure (β-thiovinyl cation). The barrier of interconversion between these two valence tautomers was calculated to be 12·8 kcal mol^–1 without geometry optimization. The pyramidal inversion at sulphur in the thiirenium ion was computed to be 72·9 kcal mol^–1.