School of Chemistry and Bio-21 Institute, University of Melbourne, Parkville 3010 Melbourne, Australia.
J Org Chem. 2011 Mar 18;76(6):1673-82. doi: 10.1021/jo102307v. Epub 2011 Feb 11.
Computational, solution phase, and crystal structure analysis of 2- and 4-organoselenylmethyl-substituted pyridinium ions (10a-c and 11a-c) provides strong evidence for C-Se hyperconjugation (σ(C-Se)-π*) between the C-Se σ-bond and the π-deficient aromatic ring and a through-space interaction (n(Se)-π*) between the selenium p-type lone pair and the π-deficient aromatic ring. There is also a weak anomeric-type interaction (n(Se)-σ*(CC)) involving the selenium p-type lone pair electrons and the polarized CH(2)-C(Ar) σ-bond. NBO analysis of calculated cations with varying electron demand (B3LYP/6-311++G**) show that C-Se hyperconjugation (σ(C-Se)-π*) is the predominant mode of stabilization in the weakly electron-demanding pyridinium ions (10d, 11d, 14, and 15); however, the through-space (n(Se)-π*) interaction becomes more important as the electron demand of the β-Se-substituted carbocation increases. The anomeric interaction (n(Se)-σ*(CC)) is relatively weak in all ions.
通过计算、溶液相和晶体结构分析 2-和 4-有机硒甲基取代的吡啶鎓离子（10a-c 和 11a-c），为 C-Se 超共轭（σ(C-Se)-π*）提供了有力证据，该超共轭存在于 C-Se σ 键和缺电子芳环之间，同时也存在硒 p 型孤对电子和缺电子芳环之间的隔空相互作用（n(Se)-π*）。此外，还有涉及硒 p 型孤对电子和极化 CH(2)-C(Ar) σ 键的弱端基型相互作用（n(Se)-σ*(CC)）。对具有不同电子需求的计算阳离子（B3LYP/6-311++G**）进行 NBO 分析表明，在电子需求较弱的吡啶鎓离子（10d、11d、14 和 15）中，C-Se 超共轭（σ(C-Se)-π*）是主要的稳定模式；然而，随着 β-硒取代碳正离子的电子需求增加，隔空相互作用（n(Se)-π*）变得更加重要。在所有离子中，端基相互作用（n(Se)-σ*(CC)）相对较弱。
