INVESTIGATION ON FORMATION AND CHARACTERISTIC REACTIONS OF DISTONIC CATION RADICALS

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Upon irradiation of 9, 10-dicyanoanthracene (DCA) contained in oxygen-saturated acetonitrile solution of unsymmetrically substituted benzophenone oxime O-methyl ethers, gave rise to the formation of one geometrical isomer around the C=N double bond. Considering the presence of a 1 to 1 mixture of the isomers in the starting material, the phenomenon is quite noteworthy. The same type of the reaction was also observed in the case of the corresponding olefinic compounds. On the basis of some controlled experiments, a superoxide radical is supposed to play a crucial role to show such an unprecedented photoisomerization. In line with the product study, we have performed the molecular orbital calculations to survey most plausible intermediate in the reaction. As a result, the requirements for leading the so-called one-way isomerization of the unsymmetrically 1, 1-disubstituted double bonds are as follows : (1) the presence of an aryl group having a strong electron-donating nature, (2) the pr … More esence of a sterically bulky group at the 2-position, and (3) the presence of another aryl group having a tendency of stabilization due to the formation of a benzylic radical. Computer simulations suggested to be a distonic cation radical as the most plausible intermediate for the reaction. Once a single electron transfer occurred between a photoexcited DCA and the substances, the ion radicals are formed. The resulting DCA anion radical reacted with oxygen to be transformed to a neutral DCA and superoxide. Meanwhile, the starting olefinic compound is altered to the corresponding cation radical. Since the cation radical has a distonic nature, the structure is a geometrically unsymmetrical one of which a cationic part is delocalized in the molecular framework consisted with the aryl group and the double bond. In the cation radical, the radical part is only delocalized at another vertically standing aryl group against the rest of the molecular framework. The superoxide reacted with the double bond and when it forms the dioxetane-like molecules, the recipient double bond cannot help rotating the predetermined direction owing to the presence of the vertically standing benzylic radical moiety. Mechanistic details and other reactions of the relevant diatonic cation radicals have been also studied Less