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Nuclear magnetic resonance spectroscopy. Variable-temperature 13C and 19F study of the chair-chair interconversion of 1,1,3,3-tetramethylcyclohexane and gem-difluoro-1,1,3,3-tetramethylcyclohexanes

Doddrell, David and Charrier, Claude and Hawkins, Bruce L. and Crain, W.O. and Harris, Leland and Roberts, John D. (1970) Nuclear magnetic resonance spectroscopy. Variable-temperature 13C and 19F study of the chair-chair interconversion of 1,1,3,3-tetramethylcyclohexane and gem-difluoro-1,1,3,3-tetramethylcyclohexanes. Proceedings of the National Academy of Sciences of the United States of America, 67 (3). pp. 1588-1592. ISSN 0027-8424. http://resolver.caltech.edu/CaltechAUTHORS:DODpnas70a

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Abstract

A variable-temperature, proton noise-decoupled, 13C nmr spectral study of the chair-chair interconversion in 1,1,3,3-tetramethylcyclohexane has demonstrated the utility of 13C spectra for probing conformational equilibria. There is a much larger chemical-shift difference between the carbons of axial and equatorial methyl groups than between the protons of these methyl groups, 133 Hz compared to 7.5 Hz. Comparison of the activation parameters determined from the 13C spectra of 1,1,3,3-tetramethylcyclohexane with those determined from a variable-temperature 19F study on 2,2,6,6-tetramethyl-1,1-difluorocyclohexane shows that the introduction of a gem-difluoro group into the ring causes significant steric interactions. The 13C chemical shifts for 1,1,3,3-tetramethylcyclohexane reflect the importance of the methyl-methyl 1,3-diaxial interactions.


Item Type:Article
Additional Information:Copyright © 1970 by the National Academy of Sciences. Communicated September 3, 1970. Supported by the National Science Foundation. Contribution no. 4083 from the Gates and Crellin Laboratories.
Record Number:CaltechAUTHORS:DODpnas70a
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:DODpnas70a
Alternative URL:http://www.pnas.org/cgi/content/abstract/67/3/1588
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4335
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:18 Aug 2006
Last Modified:26 Dec 2012 08:58

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