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含有9,10 -二氰蒽（DCA）辐照后，在C=N双键周围形成一个几何异构体。考虑到起始原料中异构体的1比1混合物的存在，这种现象是相当值得注意的。在相应的烯烃化合物中也观察到相同类型的反应。在一些对照实验的基础上，超氧自由基被认为在这种前所未有的光异构化中起着至关重要的作用。根据产物的研究，我们进行了分子轨道计算，以调查反应中最可能的中间体。因此，导致所谓的单向异构化的不对称1,1 -二取代双键的要求如下：(1)存在一个具有强给电子性质的芳基，(2)在2位有更大的空间体积基团的本质，(3)存在另一个芳基，由于苯基的形成而具有稳定化的趋势。计算机模拟表明，该反应最可能的中间产物是一个双离子阳离子自由基。一旦在光激发的DCA和物质之间发生单个电子转移，离子自由基就形成了。生成的DCA阴离子自由基与氧反应，转化为中性DCA和超氧化物。同时，起始烯烃化合物转变为相应的阳离子自由基。由于阳离子自由基具有二向性，因此在由芳基和双键组成的分子框架中，阳离子部分离域，是一种几何不对称结构。在阳离子自由基中，自由基部分只离域在另一个垂直站立的芳基上，与分子框架的其余部分相对。超氧化物与双键反应，当形成二氧乙烷类分子时，由于存在垂直存在的苯基基团，受体双键不得不沿预定方向旋转。有关全音阶阳离子自由基的机理细节和其他反应也得到了较少的研究

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