THE TILT AND ASYMMETRY OF METHYL GROUPS IN ASYMMETRIC ENVIRONMENTS
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Date
1977
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Ohio State University
Abstract
Numerous microwave spectroscopic studies of compounds with methyl groups in asymmetric environments have shown small but consistent tilts of the methyl group. An interpretation of this tilt and of the internal asymmetry of such groups has been sought by means of ab initio studies of a variety of geometry-optimized conformations of methylamine, nitrosomethane, methanol, and methylborine. Constraining parts of the molecules to non-equilibrium geometries and allowing the remainder to seek the minimum energy structure provides additional data beyond those available from experimental studies of the stable forms. Localized orbitals and Mulliken population analyses are used in further examination of the electronic structures. The methyl tilt can be interpreted as a combination of bond-bond repulsions between the C-H and X-H bond and between the X-H bonds and the lone pair. Both are important, although the C-H $\cdots$ X-H interaction is dominant. The observed asymmetric differences in the C-H bond lengths will also be discussed.""
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Author Institution: Department of Chemistry, The University of Texas