Physical Sciences and Mathematics Commons^™

Is Hyperconjugation Responsible For The "Gauche Effect" In 1-Fluoropropane And Other 2-Substituted-1-Fluoroethanes?, Paul R. Rablen, R. W. Hoffman, D. A. Hrovat, W. T. Borden

Chemistry & Biochemistry Faculty Works

The energies and geometries of a series of 2-substituted-1-fluoroethanes were computed at the MP2/6-311++G**(6D)//MP2/6-31+G* level of theory for both the maxima and minima of the rotation about the C-C bond. The results did not support the predictions of a hyperconjugative model, that both 1,2-difluoroethane and 1-chloro-2-fluoroethane would strongly prefer a gauche conformation, and that 1-fluoro-2-silylethane would strongly prefer an anti conformation. The existence of competing electrostatic interactions between the fluorine and the substituents at C-2 was indicated by the detailed geometries of the gauche conformers and by the calculated sensitivity of the gauche-anti energy differences to the presence of a …