Multiple buttressing interactions : enantiomerization barrier of tetrakis(pentamethylphenyl)ethene
Multiple buttressing interactions : enantiomerization barrier of tetrakis(pentamethylphenyl)ethene
复制标题
多重支撑相互作用：四（五甲基苯基）乙烯的对映异构化屏障
DOI：
10.1021/jo00097a063
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发表时间：
1994
影响因子：
3.6
通讯作者：
Z. Rappoport
中科院分区：
文献类型：
--
作者：
Katsuhiro Maeda;Y. Okamoto;Orly Toledano;D. Becker;S. Biali;Z. Rappoport
支撑效应是间接位阻效应，当一个大取代基与直接参与位阻相互作用的基团相邻时可能发生。引入潜在的支撑取代基可能会影响化学反应性、平衡和/或旋转势垒，因为它阻碍了未取代分子中空间拥挤基团的空间缓解模式（如键角的扩大）。在旋转过程中，支撑效应通常会导致势垒增加（“正常”支撑效应），但当基态受影响最大时，会导致较低的旋转势垒（“逆支撑效应”）。我们最近研究了二芳基和三芳基双键体系的支撑效应。对于系统1,4个m-Br或m-Me基团的引入对基态几何结构的影响较小，对两个观测到的旋转过程的影响较小。随着元取代基的引入，单环翻转过程的势垒增加，而双环翻转过程的势垒降低。3 b
Buttressing effects are indirect steric effects which may occur when a bulky substituent is adjacent to a group directly involved in steric interactions. 1 The introduction of a potentially buttressing substituent may affect chemical reactivity, equilibria, and/or rotational barriers by hindering modes of steric relief (such as the widening of bond angles) which are available in the unsubstituted molecule for the sterically crowded group. In the case of rotational processes, buttressing effects usually result in an increased barrier (a “normal” buttressing effect), but when the ground state is the one mostly affected, a lower rotational barrier results (an “inverse buttressing ef-fect”). 2 We have recently studied buttressing effects on di-and triaryl doubly bondedsystems. 3 For systems 1, the introduction of four m-Br or m-Me groups resulted in minor effects on the ground-state geometry and in moderate effects on the two observed rotational processes. The barrier for the one-ring flip process increased with the introduction of the meta substituents, while the barrier for the two-ring flip decreased. 3b