Directing power of cyclobutenoid annelations on the double bonds of planar cyclooctatetraenes.
Directing power of cyclobutenoid annelations on the double bonds of planar cyclooctatetraenes.
复制标题
环丁烯环对平面环辛四烯双键的导向能力。
DOI：
10.1021/ja017209c
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发表时间：
2002
影响因子：
15
通讯作者：
Siegel,JayS
中科院分区：
文献类型：
--
作者：
Baldridge,KimK;Siegel,JayS
采用从头算和混合密度泛函量子力学方法研究了一系列双原子桥稠环辛四烯的结构和能量。估计了各附件对exo/endo相对能量的贡献。通过比较各种桥的组成，可以找出一种给定类型的附件的关键指导因素，如应变，电负性，或循环电子计数。总的来说，电子计数和Clar/罗宾逊规则的基本组成部分很好地预测了外向/内向偏好。具体来说，三个4-e-Hückel系统（CH−CH，NH−BH和NH−C（O））显示出占优势的外型，而三个4 n + 2 Hückel对应物（C（O）−C（O），BH−BH和平面NH−NH）显示出对内型的共同偏好。这些内型系统的作用就像四个独立的四元“芳香”环通过“单键”连接。基于轮烯中碳原子的有效杂化（本特规则）的分析为它们特定的轮烯几何结构中的微妙趋势提供了理论基础。
Ab initio and hybrid density functional quantum mechanical computations are applied to the structure and energetics of a series of two-atom-bridge annelated cyclooctatetraenes. The contribution of each annelation to the exo/endo relative energy is estimated. Key directing factors for a given type of annelation, such as strain, electronegativity, or cyclic electron count, can be sorted out by comparison of various bridge compositions. Overall, electron count and the essential components of the Clar/Robinson rule work well to predict the exo/endo preferences. Specifically, three 4-e-Hückel systems (CH−CH, NH−BH and NH−C(O)) display dominant exo forms whereas the three 4n+ 2 Hückel counterparts (C(O)−C(O), BH−BH, and planar NH−NH) display a common preference for endo. These endo systems act like four independent four-membered “aromatic” rings linked by “single” bonds. An analysis based on the effective hybridization of carbon atoms in the annulene (Bent's rule) provides a rationale for subtle trends in their specific annulene geometry.