Charge Transfer Interaction and Complex Formation of Free Radicals

本课题利用激光闪光光解技术研究了二苯甲酮酮基自由基与胺的配合物形成及配合物的衰变速率。二苯甲酮酮基自由基是由溶剂分子、环己烷或胺三联体二苯甲酮的氢原子抽离反应形成的。激发激光器为308 nm XeCl准分子激光器。在二苯甲酮环己烷溶液中加入脂肪族胺后，其瞬态吸收峰位置较游离二苯甲酮酮酮基偏移5 ~ 10 nm，光谱形状变宽。这些事实表明，酮基与脂肪胺形成配合物。另一方面，芳香胺中的N，N-二甲基苯胺没有表现出对酮基径向的瞬时吸收，这表明酮基自由基会与N，N-二甲基苯胺发生反应。用反式吸收法测定了基自由基配合物的衰变。复合体的形成使衰变速度变慢；在我们的实验条件下，在30μs左右，游离酮自由基几乎完全消失，但在40μs后，胺-酮自由基络合物仍然存在。对三乙胺和三正丙胺配合物进行了动力学分析。两种自由基配合物的衰变均遵循二阶衰变规律，表明自由基配合物与游离基自由基一样，通过重组反应生成苯并纳科尔而消失。得到的速率常数分别比游离基的速率常数小0.5和0.45倍。结果表明，配合物的形成使游离基自由基的速率常数降低了约一半，三正丙胺配合物的速率常数小于三乙胺配合物的速率常数，表明胺的体积越大，复合速率越慢。结果表明，胺类化合物对反应中心起阻碍作用，抑制了复合反应。少

In this project, the complex formation of the benzophenone ketyl radical with amines and the decay rates of radical complexes have been studied with the laser flash photolysis technique. The benzophenone ketyl radicals were formed by the hydrogen atom abstraction reaction of triplet benzophenone from solvent molecules, cyclohexane, or amines. The excitation laser used was a 308 nm XeCl excimer laser. When aliphatic amines were added to the cyclohexane solutions of benzophenone, the peak position of transient absorption shifted to red by 5-10 nm and the spectral shapes became broad compared with that of free benzophenone ketyl radical. These facts indicate that the ketyl radical makes complexes with aliphatic amines. On the other hand, one of the aromatic amines, N,N-dimethylaniline, did not show the transient absorption of the ketyl radial, which suggested that the ketyl radical would react with N,N-dimethylaniline.The decays of complexes of the ketyl radical were measured by the trans … More ient absorption at the peak position. The decay rate became slow by the complex formation ; under our experimental conditions, the free ketyl radical almost completely disappeared within about 30μs, but the complexes of amine-ketyl radical survived after 40μs. The kinetic analyses were carried out on triethylamine and tri-n-propylamine complexes. The decays of both radical complexes followed the second order decay law, which indicates that the radical complexes disappeared through the recombination reaction forming benzpinacole like the free ketyl radicals do. The rate constants obtained are 0.5 and 0.45 times smaller than that of the free ketyl radical, respectively. It is revealed that the rate constant decreases about half of the free ketyl radical by the complex formation and that of the tri-n-propylamine complex is smaller than that of triethylamine complex, indicating more bulky amine makes the recombination rate slower. It is concluded that the amines work to hinder the reaction center and supress the recombination reaction. Less