Conformational preference of chlorothioformate species: molecular structure of ethyl chlorothioformate, ClC(O)SCH 2 CH 3 , in the solid phase and NBO analysis

Abstract

The molecular structure of ethyl chlorothioformate, ClC(O)SCH2CH3, has been investigated in the solid phase by X-ray diffraction analysis at low temperature using a miniature zone-melting procedure and IR laser radiation. The crystalline solid consists exclusively of molecules with thesynperiplanar conformation with respect to the CO double bond and the SC single bond, and gauche orientation of the ethyl group (syn-gauche). These results coincide with previous studies devoted to gas-phase conformational properties. The conformational preference for the ClC(O)SY (Y = Cl, CF3, CH3 and CH2CH3) series of molecules was rationalized using the natural bond orbital (NBO) scheme. It was found that both resonance (mesomeric) and anomeric (hyperconjugation) intermolecular charge-transfer interactions are important for describing the syn/anti equilibrium, also illustrating the effect of electronegativity of the substituent in the conformation preference of the ClC(O)S moiety. On the basis of the atoms in molecules (AIM) theory, intermolecular interactions have been characterized in the B3LYP/6-31G** periodic boundary electron density.