Jump to main content
Jump to site search

Issue 8, 1999
Previous Article Next Article

Is hyperconjugation responsible for the “gauche effect” in 1-fluoropropane and other 2-substituted-1-fluoroethanes?

Abstract

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 gaucheanti energy differences to the presence of a polar solvent. However, Fourier analyses of the torsional potential energies were wholly consistent with hyperconjugative electron donation into the C–F σ* orbital contributing to the conformational preferences of these 1-fluoroethanes. Fourier analyses also showed that hyperconjugation contributes to the small variations in C–C and C–F bond lengths and in fluorine atomic charges that were computed. The torsional potential energies, variations in geometry and atomic charge, and sensitivity to solvent were all in accord with the expected ranking of hyperconjugative electron donating ability of bonds to carbon, C–Si > C–H > C–C > C–Cl > C–F.

Back to tab navigation

Supplementary files

Article information


J. Chem. Soc., Perkin Trans. 2, 1999, 1719-1726
Article type
Paper

Is hyperconjugation responsible for the “gauche effect” in 1-fluoropropane and other 2-substituted-1-fluoroethanes?

P. R. Rablen, R. W. Hoffmann, D. A. Hrovat and W. Thatcher Borden, J. Chem. Soc., Perkin Trans. 2, 1999, 1719 DOI: 10.1039/A901974J

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.


Search articles by author

Spotlight

Advertisements