MOLECULAR-CONFORMATIONS AND ROTATION BARRIERS OF 2-HALOGENOETHANETHIOLS AND 2-HALOGENOETHANOLS - AN AB-INITIO STUDY

The molecular geometries of all the possible conformations of 2-halogenoethanethiols and 2-halogenoethanols (F, Cl, Br, I) have been fully optimized at the ab initio MP2/6-31G** level (for Br and I the LANL1DZ basis was adopted). Whilst for all 2-halogenoethanols and for 2-fluoroethanethiol the Gg' structure was found to be the most stable, the Tg rotamer is favoured for 2-chloro-, 2-bromo- and 2-iodo-ethanethiols. In these latter molecules the hydrogen-bond strength seems to be insufficient to overcome the non-bonded repulsive interactions and to stabilize the Gg' conformer. The rotation barriers around the C(1)-C(2) bond are rather high, whilst those concerning the SH and OH groups are generally small and of similar size.