Effect of Conjugation on Electron Distributions. Separation of σ and π Terms

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• 作者：Kenneth B. Wiberg ; Michael J. Frisch
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2016
• 出版时间：March 8, 2016
• 年：2016
• 卷：12
• 期：3
• 页码：1220-1227
• 全文大小：645K
• ISSN：1549-9626

文摘

The ground states of unsaturated molecules with Cb>sb> symmetry have separate σ and π molecular orbitals. This makes it possible to separately calculate the σ and π Hirshfeld populations and to analyze the effect of structural changes in more detail. A number of types of compounds have been studied: vinyl derivatives, 1-substituted hexatrienes, phenyl derivatives, and six-membered ring heterocycles. The results are shown as plots of changes in population vs atoms. The σ and π components vary widely, depending on π conjugation, σ inductive effects, and σ/π polarization. When an electron withdrawing group is attached to an alkene carbon, significant σ density is transferred to it, and to compensate π density is transferred to the substituent. Such interactions are similar to those found when a carbonyl or other ligands are attached to a metal.