Rotational Barriers of Methyl Fluorosulfonate and Chlorosulfonate: Comparison between Computational Methods and Experiment

Molecular structures derived from microwave and electron diffraction experiments on methyl fluorosulfonate and methyl chlorosulfonate were ambiguous as to whether gauche or anti conformations were most stable. Rotational barriers are computed at the SVWN/6-31G**, BP86/6-31G**, B3LYP/6-31G**, and localized MP2/6-31G** levels. Calculations are in agreement that the gauche conformation is a minimum. The syn and anti rotational barriers relative to the gauche minimum are determined and found to be attractive dominant. Optimized geometry differences among the different methods are examined.