Substituent effects on the rate of decay of p-benzosemiquinone anion radicals

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The rates of decay of p-benzosemiquinone radicals produced by reduction of the corresponding quinone at a platinum electrode have been studied by electron spin resonance. Nine monosubstituted quinones were studied with regard to the substituent effect on the decay rate in absolute methanol. The rates were found to be markedly accelerated by electron-withdrawing groups, and have been correlated by a Hammett plot of the logarithm of the decay rate vs. the σp0 values for the substituents. The decay reactions are all second-order in radical concentration, and a reaction mechanism has been proposed that is consistent with the experimental observations.

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Journal of Physical Chemistry