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Abstract
The kinetics of thermal bimolecular reactions of nitroxyl radicals with hydrazo compounds have been studied in a nematic liquid crystal. The experimental reaction rate constant in the pretransition region of the isotropic phase and in the mesophase has been found to show a positive deviation from the Arrhenius dependence obtained in the isotropic phase at higher temperatures. A method is proposed for a quantitative description of the temperature dependence of the experimental rate constant in the mesophase, based on the assumption of a decrease in the activation energy in the nematic phase, as compared with the isotropic phase. Consideration is given to the influence of nematic ordering on the activation energy of the reactions studied, conforming to the values of the parameters found from the experimental data. Models accounting for the existence of local ordering fluctuations are proposed for a quantitative description of the temperature dependence of the experimental rate constant in the isotropic phase. These are based on an approximate representation of a liquid crystal above the clearing point as a combination of isotropic and nematic regions. This makes it possible to estimate the size of the minimal region of nematic ordering that a given reaction is sensitive to.