A B3LYP study of the effects of phenyl substituents on 1,5-hydrogen shifts in 3-(Z)-1,3-pentadiene provides evidence against a chameleonic transition structure
A B3LYP study of the effects of phenyl substituents on 1,5-hydrogen shifts in 3-(Z)-1,3-pentadiene provides evidence against a chameleonic transition structure
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DOI：
10.1021/ja048708r
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发表时间：
2004-08-18
影响因子：
15
通讯作者：
Borden, WT
中科院分区：
文献类型：
--
作者：
Hayase, S;Hrovat, DA;Borden, WT
用B3LYP/6-31G*方法研究了一个或两个苯基取代对3-(Z)-1，3-戊二烯(1)中1，5-氢转移的活化热和过渡结构几何构型的影响。苯基取代基对实验测得的活化热的影响预计是相当大的，范围近10千卡/摩尔。然而，如果通过比较顺式构象的活化焓来考虑反应物跨体异构体的空间效应之间的差异，那么苯基取代基对势垒高度和TS几何构型的影响的电子组分的尺寸是相当小的。与COPE重排中的TS不同，1，5-氢转移的TS本质上不是高度可变的，并讨论了1，5-氢转移TS不是变色龙的原因。
The effects of one or two phenyl substituents on the activation enthalpy for a 1,5-hydrogen shift in 3-(Z)-1,3-pentadiene (1) and on the geometry of the transition structure (TS) have been investigated by B3LYP/6-31G* calculations. The phenyl-substituent effects on the experimentally measured activation enthalpies are predicted to be sizable, spanning a range of nearly 10 kcal/mol. However, if differences between steric effects in the transoid isomers of the reactants are factored out by comparing the activation enthalpies in the cisoid conformers, the electronic components of the phenyl-substituent effects on both the barrier heights and the TS geometries are found to be quite modest in size. Unlike the TS in the Cope rearrangement, the TS for a 1,5-hydrogen shift in 1 is not highly variable in nature, and the reason the 1,5-hydrogen shift TS is not chameleonic is discussed.