Ring Inversion in Cyclohexyl Radical

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Abstract
The ESR spectrum of cyclohexyl radical in solid cyclohexane has been studied, during irradiation, between —85° and 0°C. Continuous electron irradiation is necessary because diffusion and recombination of the radicals occurs in this temperature interval. The broadening of certain of the lines as the temperature is raised has been interpreted in terms of an interconversion between two forms of the radical. The change of linewidth (or alternately, peak height) with temperature corresponds to an activation energy for the interconversion of 4.9±0.5 kcal/mole. The magnitude of the barrier, though smaller than that in cyclohexane itself, suggests that the interconversion is between the two chair forms of the radical. In the calculation of correlation times from the broadening, it was necessary to develop expressions which are applicable to spectra with Gaussian lines. This treatment is verified by the agreement of the data for C6H11· and C6D11·.