Conformations and thermodynamic properties of sulfur homocycles. 1. The S-5, S-6, S-7, and S-8 molecules

Results of B3LYP/6-311G* and MP2/6-311G* electronic structure calculations provide a comprehensive characterization of all the conformers of the S-5, S-6, S-7, and S-8 homocycles and elucidate their interconversions. The S-5 ring is confirmed to exist exclusively in a highly fluxional C-s conformati on. Two conformers of the S-6 homocycle, linked through two transition stat es, are identified: the D-3d structure corresponding to a global energy min imum and the higher-energy species possessing C-2 nu symmetry. The S-7 ring is found to adopt one of two highly fluxional C-s conformations that are s eparated by a substantial barrier. The complete set of the conformers of th e S-8 homocycle, which consists of the C-2 nu, C-2, C-s (and possibly also C-2h) structures in addition to the low-energy D-4d species, is uncovered.