The impact of resonance stabilization on the intramolecular hydrogen-atom shift reactions of hydrocarbon radicals.
The impact of resonance stabilization on the intramolecular hydrogen-atom shift reactions of hydrocarbon radicals.
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DOI：
10.1002/cphc.201500396
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发表时间：
2015-08
期刊：
影响因子：
--
通讯作者：
Kun Wang;Stephanie M. Villano;A. Dean
中科院分区：
文献类型：
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作者：
Kun Wang;Stephanie M. Villano;A. Dean
用CBS-QB 3电子结构计算方法研究了烯基和烯丙基自由基的分子内H原子位移反应。在第一组反应中，烷基自由基位点被转化为烯丙型自由基位点。在第二组中，一个烯丙基自由基转化为另一个烯丙基自由基。的背景下，本森型模型的结果进行了讨论，以检查的影响的过渡态部分共振稳定的活化能和指前因子。在大多数情况下，活化能相对于类似的烷基自由基的差异主要是由于活化能的双分子反应组分的势垒。对于第一组反应，相对于烷基自由基类似物，存在额外的熵损失。这种额外的熵损失可能小于一些先前的估计。第二组反应的指前因子通常与类似的烷基自由基反应的指前因子相似（一旦考虑了过渡态中的双键）。
A series of intramolecular H-atom shift reactions of both alkenyl and allylic radicals were investigated by using CBS-QB3 electronic structure calculations. In the first set of reactions, an alkyl radical site was converted into an allylic radical site. In the second set, an allylic radical was converted into another allylic radical. The results are discussed in the context of a Benson-type model to examine the impact of the transition-state partial resonance stabilization on both the activation energies and the pre-exponential factors. In most cases, the differences in the activation energies relative to those for the analogous alkyl radicals are primarily due to the barriers of the bimolecular reaction component of the activation energy. For the first set of reactions, there is additional entropy loss relative to the alkyl radical analogues. This additional loss of entropy may be smaller than some previous estimates. The pre-exponential factors for the second set of reactions are generally similar to those of the analogous alkyl radical reactions (once the double bond in the transition state is accounted for).