Molecular structures of gauche and trans conformers for oxalyl chloride: ab initio and DFT calculations

Abstract

Ab initio and density functional theory (DFT) methods are applied to investigate the molecular structure and conformational nature of oxalyl chloride. The calculations which include the effects of the electron correlation at the MP2 and B3LYP levels with the basis sets much larger than 6-311+G(d) can reproduce the previous experimental evidence about the gauche conformation. It has been verified that the van der Waals repulsion between oxygen and chlorine atoms as well as the πCO→σ∗CCl, σCCl2→π∗CO, and nCl,O→π∗CO interactions plays an important role in explaining the existence of rather a unique gauche conformer. The potential energy surface computed at the B3LYP level is relatively more reliable to explain the existence of a gauche conformer than that computed at the MP2 level. In addition, the C–C bond torsional angles computed at the B3LYP levels are rather stationary around 88° as the size of the basis set is increased.