Gauche and trans conformers of 1,2-dihaloethanes:: A study by ab initio and density functional theory methods

This work deals with a systematic study of the gauche and trans conformers of 1,2-dihaloethanes (XCH2CH2X, X=F, Cl, Br and I). The methods used are Hartree-Fock (HF), second order Moller-Plesset theory (MP2) and density functional theory (DFT). The basis sets used are 6-311+(d,p) and 6-311++(d,p) except for 1,2-diiodoethane where 3-21G is used. The functional used for DFT method is B3LYP. G2/MP2 calculations have also been done. The results reveal that there is a preference for the trans conformer except for 1,2-difluoroethane. The energy difference between the gauche and trans forms generally increases with an increase in the size of the halogen. Vibrational analysis has also been carried out.