环戊二烯分子内 π电子的离域是失稳定的──分子内 π和σ轨道分离法  

The Destabilization of π-Electron Delocalization in Cyclopentadiene──A Method of Separating out of Its π, π-like and σ Fragment Molecular Orbitals

作　　者：虞忠衡[1] 宣正乾[1] 

机构地区：[1]中国科学院化学研究所分子动态与稳态国家重点实验室,北京100080

出　　处：《高等学校化学学报》2000年第3期421-426,共6页Chemical Journal of Chinese Universities

基　　金：国家重点基础研究发展规划项目!(批准号 :G19980 10 10 0 );国家自然科学基金!(批准号 :2 95 72 0 74;39890 390 );中国科学院院长

摘　　要：为环戊二烯分子中非平面片断的片断轨道的建立提供了一个新的方法和计算程序 .分子内的Morokuma作用能的计算表明 ,“π电子的离域是失稳定的”与“离域的π体系是失稳定的”是两个完全不同的概念 .π电子离域的结构效应完全取决于 σ体系对离域的作用 .在环戊二烯分子中 ,π电子的离域和离域的π体系均是失稳定的 .在苯分子中 ,π电子的离域是失稳定的 ,它的离域π体系也是失稳定的 .但在 D6 h中 ,离域 π体系是“较小失稳定”的 .应该强调 π与 σ电子间空间作用对分子性能的重大影响 ,以改变经典有机结构理论重 π轻A procedure for separating out of π, π like and σ fragment molecular orbitals(FMO) was established, and it provides for cyclopentadiene a complete FMO basis set in which all FMOs have correct electron occupancies. Based on our new method, the Morokuma energy partition provides, in the framework of ab initio SCF MO computation at the STO 3G level, the various π and σ energies associated with the inter and intrafragment interactions. The π electronic delocalization is destabilization in cyclopentadiene, and its delocalized π system is also destabilized. In the case of benzene, its QMRE is stabilizing. However, it is the σ framework of benzene, rather than the π system itself, to be strongly stabilized, revealing the benzene is σ aromatic. It should be emphasized that the σ π space interactions, expressed in terms of the Coulomb J σπ and exchange K sp integrals, have significant effects on the molecular behaviour.

关 键 词：共轭效应 轨道作用 环戊二烯 π电子离域 

分 类 号：O624.12[理学—有机化学] O641.122[理学—化学]