Molecular structure, conformational stability and cis effect of 1,4-dichlorobutadiene — a quantum chemical study

Abstract

The conformational equilibrium of 1,4-dichlorobutadiene molecule has been investigated using ab initio and density functional theory calculations at Hartree–Fock self consistent filed theory (HF-SCF), Møller–Plesset perturbation theory (MP2), B3LYP and B3PW91 levels of theory. The three larger basis sets have been used to study the cis effect of the molecule. The MP2 and B3PW91 methods predicted that the cis– cis conformer is more stable and the former method was able to predict the order of stability in accordance with the experimental results. The HF-SCF and B3LYP methods have failed to predict the cis– cis conformer of 1,4-dichlorobutadiene as the most stable structure even with the higher basis set 6-311++G ∗∗. The relative stability of cis– cis conformer is found to be a consequence of the spectroscopic trans destabilization. The principle of maximum hardness has been tested for the cis effect. The complete frequency analysis has been performed for three isomers at MP2/6-31G ∗ level of theory.