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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Rate constants for 1,5- and 1,6-hydrogen atom transfer reactions of mono-, di-, and tri-aryl-substituted donors, models for hydrogen atom transfers in polyunsaturated fatty acid radicals
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Rate constants for 1,5- and 1,6-hydrogen atom transfer reactions of mono-, di-, and tri-aryl-substituted donors, models for hydrogen atom transfers in polyunsaturated fatty acid radicals

机译：单，二和三芳基取代的供体的1，5-和1,6-氢原子转移反应的速率常数，多不饱和脂肪酸自由基中氢原子转移的模型

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摘要

Rate constants for 1,5- and 1,6-hydrogen atom transfer reactions in models of polyunsaturated fatty acid radicals were measured via laser flash photolysis methods. Photolyses of PTOC (pyridine-2-thioneoxycarbonyl) ester derivatives of carboxylic acids gave primary alkyl radicals that reacted by 1,5-hydrogen transfer from mono-, di-, and tri- aryl-substituted positions or 1,6-hydrogen transfer from di- and tri-aryl-substituted positions to give UV-detectable products. Rate constants for reaction's in acetonitrile at room temperature ranged from 1 x 10(4) to 4 x 10(6) s(-1). The activation energies for a matched pair of 1,5- and 1,6-hydrogen atom transfers giving tri-aryl-substituted radicals, were approximately equal, as were the primary kinetic isotope effects, but the 1,5-hydrogen atom transfer reaction was 1 order of magnitude faster at room temperature than the 1,6-hydrogen atom transfer reaction due to a less favorable entropy of activation for the 1,6-transfer reaction. Solvent effects on the rate constants for the 1,5-hydrogen atom transfer reaction of the 2-[2-(diphenylmethyl)-phenyl]ethyl radical at ambient temperature were as large as a factor of 2 with the reaction increasing in rate in lower polarity solvents. Hybrid density functional theory computations for the 1,5- and 1,6-hydrogen atom transfers of the tri-aryl-substituted donors were in qualitative agreement with the experimental results.
机译：通过激光闪光光解法测量了多不饱和脂肪酸自由基模型中1,5-和1,6-氢原子转移反应的速率常数。羧酸的PTOC（吡啶-2-硫代氧羰基）酯衍生物的光解反应生成伯烷基，这些伯烷基通过1,5-氢从单，二和三芳基取代的位置转移或1,6-氢从被二和三芳基取代的位置，可得到可检测紫外线的产物。室温下乙腈中反应的速率常数范围为1 x 10（4）到4 x 10（6）s（-1）。匹配的一对1,5-和1,6-氢原子转移产生三芳基取代的自由基的活化能与主要的动力学同位素效应大致相等，但是1,5-氢原子转移反应由于1，6-转移反应的活化熵较差，因此在室温下比1，6-氢原子转移反应快1个数量级。在室温下，溶剂对2- [2-（2-（二苯基甲基）-苯基]乙基的1,5-氢原子转移反应的速率常数的影响最大为2倍，反应速率越低，反应速率越高。极性溶剂。三芳基取代的供体的1，5-和1，6-氢原子转移的混合密度泛函理论计算与实验结果在质量上是一致的。

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