Determination of the molecular structure of ethylphosphonothioic dichloride by gas-phase electron diffraction and ab initio calculations

Abstract The molecular structure of ethylphosphonothioic dichloride, CH 3 CH 2 P (S)Cl 2 , in the gas phase has been determined from an electron diffraction study. The gas consists of an equilibrium mixture of two conformers, in which the methyl group is trans or gauche with respect to the sulfur atom, but it is not possible to measure the proportions of the two forms because of the similarity of the sulfur and chlorine scattering powers, and of the PS and PCl bond lengths. Ab initio calculations at the 3-21G* level, were therefore performed, and these indicate that the conformation should be 82% gauche and 18% trans . These proportions were then used in the electron diffraction refinements, and the calculated differences between geometric parameters, most notably in the PCC angles, are also incorporated. Refined parameters ( r a ) for the major conformer include r (PCl) 203.0(1), r (PS) 189. ∠ClPC (mean) 103.1 (5), ∠CPS 116.1 (12) and ∠ClPCl 102.0(4)°.