Energy optimization, vibrational frequencies and asymmetric potential function for internal rotation in 2-methyl-2-butenoyl fluoride and chloride

The conformational stability and structure of 2-methyl-2-butenoyl fluoride and chloride were investigated by utilizing ab initio calculations with 6-31G* basis set at RHF and MP2 levels. For both compounds, the s-trans conformer was predicted by the two levels to be slightly the lower energy form. Full optimization was performed at the transition states and the barriers to interconversion between the cis and trans conformers were calculated. The vibrational frequencies were computed at HF level and the zero-energy corrections were included into the calculated barriers. The inclusion of electron correlation in the calculations was shown to make a small change in the calculated energies and barriers, particularly in the case of the chloride.