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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photogeneration of benzhydryl cations by near-UV laser flash photolysis of pyridinium salts
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Photogeneration of benzhydryl cations by near-UV laser flash photolysis of pyridinium salts

机译：吡啶鎓盐的近紫外激光闪光光解光催化生成苯甲基阳离子

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摘要

Laser flash irradiation of substituted N-benzhydryl pyridinium salts yields benzhydryl cations (diarylcarbenium ions) and/or benzhydryl radicals (diarylmethyl radicals). The use of 3,4,5-triamino-substituted pyridines as photoleaving groups allowed us to employ the third harmonic of a Nd/YAG laser (355 nm) for the photogeneration of benzhydryl cations. In this way, benzhydryl cations can also be photogenerated in the presence of aromatic compounds and in solvents which are opaque at the wavelength of the quadrupled Nd/YAG laser (266 nm). To demonstrate the scope and limitations of this method, the rate constants for the bimolecular reactions of benzhydryl cations with several substituted pyridines were determined in acetonitrile and with water in acetone. The obtained data agree with results obtained by stopped-flow UV-vis spectroscopic measurements. The rate constants for the reaction of the 4,4'-bis[methyl(2,2,2- trifluoroethyl)amino]benzhydrylium ion with 4- (dimethylamino)pyridine were also determined in dimethyl sulfoxide, N,N-dimethylformamide, and acetone. From the secondorder rate constants, we derived the nucleophilicity parameters N and sN for the substituted pyridines, as defined by the linear free energy relationship, log k2 = sN(N + E).
机译：取代的N-苯甲酰基吡啶鎓盐的激光快速辐射产生苯甲基阳离子（二芳基碳鎓离子）和/或苯甲基自由基（二芳基甲基自由基）。使用3,4,5-三氨基取代的吡啶作为光致离去基团使我们能够使用Nd / YAG激光（355 nm）的三次谐波来进行苯甲基阳离子的光生。这样，在芳族化合物的存在下和在四倍Nd / YAG激光波长（266 nm）不透明的溶剂中，苯甲酰基阳离子也可以光生。为了证明该方法的范围和局限性，在乙腈中和用水在丙酮中，测定了苯甲基阳离子与几种取代的吡啶的双分子反应的速率常数。获得的数据与通过停止流动的紫外可见光谱测量获得的结果一致。还确定了在二甲亚砜，N，N-二甲基甲酰胺和4,4'-双[甲基（2,2,2-三氟乙基）氨基]苯甲酸根离子与4-（二甲基氨基）吡啶反应的速率常数丙酮。从二阶速率常数，我们得出了取代吡啶的亲核参数N和sN，如线性自由能关系log k2 = sN（N + E）所定义。

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