LONE PAIR POLAR BOND HYPERCONJUGATION IN CARBON-HALOGEN CHEMISTRY
LONE PAIR POLAR BOND HYPERCONJUGATION IN CARBON-HALOGEN CHEMISTRY
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DOI：
10.1021/ja00856a023
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发表时间：
1975-01-01
影响因子：
15
通讯作者：
BINGHAM, RC
中科院分区：
文献类型：
--
作者：
BINGHAM, RC
分子轨道理论表明，当X代表卤素时，邻域孤对极键超共轭(如XCH2-CH2-*-*·X-CH2=CH2)的重要性应按F<；CL<；Br<；1的顺序增加。这种模式由碳-卤键强度决定，与这种现象的价键描述所预测的模式相反。各种可用的实验数据，包括2-卤代四氢吡喃(反常效应)、2-卤代环己酮和烯丙基卤化物的构象平衡，MA‘-二甲基氨基甲酰卤化物的转动势垒，以及卤代乙酸的酸度，都支持分子轨道的解释。这些结果表明，An离子超共轭确实是一个非常真实、普遍和重要的概念。
Molecular orbital theory suggests that the Importance of vicinal lone pair-polar bond hyperconjugation (eg, XCH2-CH2-*-*·X-CH2= CH2) should increase, when X represents halogen, in the order F< Cl< Br< 1. This pattern, which is determined by the carbon-halogen bond strengths, contrasts with that predictedby the valence bond description of this phenomenon. A variety of available experimental data, including the conformational equilibriaof 2-halotetrahydropyr-ans (the anomeric effect), 2-halocyclohexanones and allyl halides, the rotational barriers ofMA'-dimethylcarbamyl halides, and the acidities of haloacetic acids, support the molecular orbital interpretation. These results serve to demonstrate that an-ionic hyperconjugation is, indeed, a very real, general, and Important concept.