Lone-pair interactions in HSSSSH

Abstract

The barriers of rotation about the central SS bond in HSSSSH and the effect of the corresponding torsional angle on all SS bond lengths were studied by ab initio methods using minimal Gaussian basis sets, augmented in the case of sulfur with d-polarization functions. The central SS bond was found to lengthen from the equilibrium value as the torsional angle approached 0 or 180°, as expected from the behaviour of the SS bond in HSSH. Simultaneously, the adjacent SS bonds became somewhat shorter. This trend is well established experimentally. A plausible explanation involves repulsion of the p-lone-pair orbitals of the neighbouring central sulfur atoms as well as hyperconjugation of the same lone-pair orbitals with the antibonding σ HS * orbitals. Both rotational barriers about the central SS bond were found to be ca. 30 kJ mol −1. This agrees with the barrier heights calculated earlier from NMR data. The performance of the basis set was investigated with HSSH.