S-ethyl thiochloroformate, ClC(O)SCH 2CH 3: Unusual conformational properties?

Abstract

The conformational equilibrium of S-ethyl thiochloroformate, ClC(O)SCH 2CH 3, was determined by vibrational spectroscopy (FTIR and FTRaman spectra), ab initio and density functional theory calculations (HF/3-21G*, HF/6-31G* and B3PW91/6-31G*). The evaluation of experimental and theoretical results suggests the existence of two conformers syn, gauche (CO double bond syn with respect to the S–C single bond and C–S single bond gauche with respect to the C–C single bond, respectively) and syn, anti, being the former most stable one. The existence of this rotational isomerism is rather unexpected for this thioester compound, owing to the known conformational equilibrium reported for some thioesters that depends on the ClCSC torsion angle. Photolysis products of the compound irradiated in adequate inert gas matrices were identified as CO, SCO, C 2H 5SCl and C 2H 5Cl.