STERIC EFFECTS - A STUDY OF A RATIONALLY DESIGNED SYSTEM
STERIC EFFECTS - A STUDY OF A RATIONALLY DESIGNED SYSTEM
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DOI：
10.1021/ja00537a036
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发表时间：
1980-01-01
影响因子：
15
通讯作者：
STERNHELL, S
中科院分区：
文献类型：
--
作者：
BOTT, G;FIELD, LD;STERNHELL, S
提出了合理设计适合于空间效应研究的体系的原则。合适的分子框架[6-本文合成了[2-X-苯基]-5-基-1，1-二甲基茚满，1]，并对33个衍生物的内旋转进行了动态核磁共振研究，结果表明：（1）对于1（Y= Me; X=卤素）的转动势垒（AG*）随X（X）的货车德瓦尔斯半径平滑单调地增加，这使得可以估算较低对称性碎片的有效势垒，（ii）转动势垒是加性贡献的总和，指定的干涉值（/H”x），其可用于预测2，2 '-二取代联苯中的转动势垒。（iii）一个简单的几何参数，表观重叠（r*），其与过渡态中骨架的畸变有关，提出并发现与2，2 ′-二取代联苯的旋转势垒有很好的线性相关性，（四）该关联式可用于联芳基化合物和其它体系中转动势垒的半定量估算。与非键合分子片段拥挤相关的能量损失。因此，对这一现象的研究必须涉及碎片的大小（通常用货车德瓦尔斯半径来定义）、碎片相互作用的系统的几何形状以及与相互作用有关的能量等概念。空间位阻形成
The principles for the rational design of systems suitablefor the study of steric effects are defined. A suitable molecular framework [6-(2-X-phenyl)-5-Yl, l-dimethylindan, 1] was synthesized and a study of internal rotation by dynamic NMR spectroscopy (DNMR) of 33 derivatives, differing principally in the nature of the molecular fragment (X), showed thefollowing,(i) For 1 (Y= Me; X= halogen) the rotational barriers (AG*) increase smoothly and monotonically with the van der Waals radius ofX (rx), which permits the estimation of effective rx for fragments of lower symmetry,(ii) The rotational barriers are the sum of additive contributions, designated interference values (/H" x), which can be used to predict the rotational barriers in 2, 2'-disubstituted biphenyls,(iii) A simple geometrical parameter, apparent overlap (r*)> which is related to the distortion of the framework in the transition state, is proposed and found to have an excellent linear correlation with the barrier to rotation in 2, 2'-disubstituted biphenyls,(iv) This correlation can be used for a semiquantitative estimation of rotational barriers in biaryls and other systems.Steric hindrance can be defined as the energy penalty associated with crowding of nonbonded molecular fragments. The studyof this phenomenon must therefore involve notions of size (typically defined in terms of van der Waals radii1) of the fragments, the geometry of the systems within which they interact, and the energy associated with the interaction (s). Steric hindrance forms a