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Ring inversion of fluorocyclohexane in its solid thiourea inclusion compound

Harris, R K and Nordon, A and Harris, K D M (1999) Ring inversion of fluorocyclohexane in its solid thiourea inclusion compound. Magnetic Resonance in Chemistry, 37 (1). pp. 15-24. ISSN 1097-458X

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Abstract

The rate of ring inversion of fluorocyclohexane in the solid inclusion compound that it forms with thiourea was studied using a variety of NMR techniques. Special use was made of F-19 NMR spectra acquired with high-power proton decoupling. Bandshape analysis was used in the range 237-300 K. The occurrence of ring inversion at lower temperatures was established by the two-dimensional EXSY method and the rates thereof were determined by selective polarization inversion. Measurements of spin-lattice relaxation in the rotating frame showed a minimum at 300 K, yielding an additional value for the ring inversion rate. Variable-temperature triple-channel C-13-{H-1,F-19} spectra were studied. It is concluded that the average activation parameters (from the F-19 work) for the forward and backward ring inversion processes are Delta H double dagger=39.4+/-2.6 kJ mol(-1) and Delta S double dagger = - 12 +/- 11 J mol(-1) K-1. The near equality of the axial and equatorial populations makes accurate determination of separate barriers for the equatorial --> axial and axial --> equatorial processes problematic. The values are discussed in relation to those for other cyclohexane derivatives in their thiourea inclusion compounds and for fluorocyclohexane in other media. The superiority of the F-19 measurements over the use of C-13 spectra is emphasized.

Item type: Article
ID code: 34642
Keywords: NMR, solid-state NMR, magic-angle spinning, fluorine-19, carbon-13, fluorocyclohexane, inclusion compound, ring inversion, chemical exchange, monosubstituted cyclohexanes, conformational properties, temperature-gradients, Chemistry, Materials Science(all), Chemistry(all)
Subjects: Science > Chemistry
Department: Faculty of Science > Pure and Applied Chemistry
Related URLs:
    Depositing user: Pure Administrator
    Date Deposited: 21 Oct 2011 10:18
    Last modified: 05 Sep 2014 12:10
    URI: http://strathprints.strath.ac.uk/id/eprint/34642

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