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Nuclear Magnetic Resonance Spectroscopy. Conformational Equilibria and Rates of Conformational Interconversion of Halogenated Ethanes

Weigert, Frank J. and Winstead, Meldrum B. and Garrels, James I. and Roberts, John D. (1970) Nuclear Magnetic Resonance Spectroscopy. Conformational Equilibria and Rates of Conformational Interconversion of Halogenated Ethanes. Journal of the American Chemical Society, 92 (25). pp. 7359-7368. ISSN 0002-7863.

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The relative ground-state energies of the rotational isomers of some halogenated ethanes and the rates and barriers to interconversions of these isomers have been determined by nuclear magnetic resonance spectroscopy. In the ethanes studied in this research, those with a single fluorine were found to have the ^(19)F resonance of the least populated conformation at highest field, while that of the most populated conformation was found at the lowest field. All three barriers for interconversion could be determined for the ethanes substituted so as to give three distinguishable conformations. For these cases it was found that the highest barrier separates the two least populated conformations and the lowest barrier separates the most stable conformations. The substances for which complete nmr line-shape analysis have given the equilibrium constants, rates, and barriers for internal rotation include 1,1,2-tribromo-1,2-dichloro-2-fluoroethane, 1,1- dibromo-1,2,2-trichloro-2-fluoroethane, 1-bromo-1,1,2,2-tetrachloro-2-fluoroethane, 1,1,2,2-tetrabromo-1-chloro-2-fluoroethane, 1,2-dibromo-1,1,2-trichloro-2-fluoroethane, 1,1,2-tribromo-1-chloro-2-fluoroethane, 1-bromo-l,1,2-trichloro-2-fluoroethanaen,d 1,2-dibromo-1,1,24richloro- 3,3,3-trifluoropropane. For those ethanes carrying five halogens other than fluorine, the barriers (to rotation) range from 13.2 to 14.8 kcal/mol, while for those with four halogens other than fluorine, the barriers range from 9.0 to 10.2 kcal/mol. The ground-state energy differences for all of the ethanes studied did not exceed 0.3 kcal/mol.

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Additional Information:© 1970 American Chemical Society. Received March 26, 1970. Supported by the National Science Foundation; National Science Foundation Predoctoral Fellow, 1965-1968; Public Health Service Special Research Fellow, 1967-1968.
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NSF Predoctoral FellowshipUNSPECIFIED
Public Health ServiceUNSPECIFIED
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Caltech Gates and Crellin Laboratories of Chemistry4027
Issue or Number:25
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Official Citation: Nuclear magnetic resonance spectroscopy. Conformational equilibria and rates of conformational interconversion of halogenated ethanes Frank J. Weigert, Meldrum B. Winstead, James I. Garrels, and John D. Roberts Journal of the American Chemical Society 1970 92 (25), 7359-7368 DOI: 10.1021/ja00728a020
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60998
Deposited By: Ruth Sustaita
Deposited On:13 Oct 2015 21:17
Last Modified:03 Oct 2019 09:03

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