INVESTIGATION ON FORMATION AND CHARACTERISTIC REACTIONS OF DISTONIC CATION RADICALS

不对称取代二苯甲酮肟O-甲基醚的氧饱和乙腈溶液中的9，10-二氰基并[9，10-二氰基菲](DCA)在光照下，在C=N双键附近形成一个几何异构体。考虑到起始原料中存在1：1的异构体混合物，这一现象相当值得注意。在相应的烯烃化合物中也观察到了相同类型的反应。在一些受控实验的基础上，超氧自由基被认为是显示这种前所未有的光异构化的关键作用。与产物研究相一致，我们进行了分子轨道计算，以考察反应中最可能的中间体。因此，引导不对称1，1-二取代双键的所谓单向异构化的要求如下：(1)具有强给电子性的芳基的存在，(2)Pr…在2-位上更多地存在空间大的基团，以及(3)由于形成苄基而具有稳定趋势的另一个芳基的存在。计算机模拟表明，该反应最可能的中间体是远位阳离子自由基。一旦在光激发的DCA和物质之间发生了单电子转移，就形成了离子自由基。生成的DCA阴离子自由基与氧反应生成中性的DCA和超氧化物。同时，起始的烯烃化合物被改变为相应的阳离子自由基。由于阳离子自由基具有远位性质，其结构是几何不对称的，其中阳离子部分离域在由芳基和双键组成的分子骨架中。在阳离子自由基中，自由基部分只离域在与其余分子骨架垂直排列的另一个芳基上。超氧化物与双键反应，当它形成二氧杂环己烷类分子时，由于垂直站立的苄基自由基部分的存在，受体双键不能帮助旋转预定的方向。相关的全光性阳离子自由基的机理细节和其他反应的研究也较少

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