ELEMENTARY ACTS OF PHOTOREACTIONS OF 2,6-DIPHENYL-1,4-BENZOQUINONE IN VARIOUS SOLVENTS

Abstract

In order to determine the effect of the polarity of solvents on the reactivity and the course of the reactions of semihinone radicals, their complexes, this study of 2,6-diphenyl-1,4-benzoquinone, (class of substituted benzoquinones) and its dimer D was carried out. It was found that in the NMR spectrum of the dimer solution, with increasing temperature, the lines widen, and there is one wide line close to the chemical shift to the protons of the meta-groups of quinone. The NMR spectrum of a solution D in deuterochloroform at low temperatures contains lines corresponding to the aromatic part of the protons in the meta position, respectively (7.05 M.d, 6.89 M.d.). That is, the exchange process between the non-equivalent parts of the diamagnetic dimer molecule of the preceding dissociation takes place with the constant of the velocity k-1, coinciding in order of the inverse spin-spin relaxation time. The value of k-1 increases by more than an order of magnitude with the increasing polarity of the solvent. This effect is due to the stronger solvent solvation of the activated complex in the transition state compared to the molecule. The reaction of dimerization of semiquinone radicals is diffusion-controlled, since the values of ∆H1≠ in all solvents differ from the activation energy of viscosity by no more than 1 kcal/M and the values of the velocity constant in 5-8 times differ from the diffusion rate constant calculated by Debye. The solvation of radicals leads to a decrease in the diffusion coefficients of radicals and, possibly, to the shielding of the reaction center, which causes a decrease in k1. With the decrease of the constant in the specified number of solvents, the stability of the radical increases, which is manifested in a symbiotic increase in the equilibrium constant K. The reason for the increase of the direct constant k1 in solvents with high permittivity is explained.