Juaristi Eusebio, Cuevas Gabriel
Departamento de Química, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apdo. Postal 14-740, 07000 México, D.F., Mexico.
Acc Chem Res. 2007 Oct;40(10):961-70. doi: 10.1021/ar6000186. Epub 2007 Jun 28.
Two-electron/two-orbital hyperconjugative interactions depend on the relative orientation of bonds and lone pairs in a molecule and are also inversely proportional to the energy difference between the interacting orbitals. Spectroscopic manifestations of stereoelectronic interactions are particularly useful experimental signatures of these effects which can be utilized for testing molecular models. Empirical observations together with theoretical interpretations in cyclohexane and six-membered heterocycles confirm the relevance of sigma C-H ax --> sigma* C-H ax , n X --> sigma* C-H ax (X = O or N), sigma C-S --> sigma* C-H eq , beta-n O --> sigma* C-H eq , sigma C(2)-H ax --> pi* CY (Y = O, S, or CH 2), and sigma C(2)-H ax --> sigma* S-O ax two-electron/two-orbital stereoelectronic interactions that weaken the acceptor (or donor) C-H bonds and attenuate the Fermi contribution to the one-bond (13)C- (1)H coupling constants.
双电子/双轨道超共轭相互作用取决于分子中键和孤对电子的相对取向，并且也与相互作用轨道之间的能量差成反比。立体电子相互作用的光谱表现是这些效应特别有用的实验特征，可用于测试分子模型。在环己烷和六元杂环中的经验观察以及理论解释证实了σ C-H轴向→σ* C-H轴向、n X→σ* C-H轴向（X = O或N）、σ C-S→σ* C-H平伏、β-n O→σ* C-H平伏、σ C(2)-H轴向→π* CY（Y = O、S或CH₂）以及σ C(2)-H轴向→σ* S-O轴向双电子/双轨道立体电子相互作用，这些相互作用会削弱受体（或供体）C-H键，并减弱费米对一键(¹³)C-(¹)H耦合常数的贡献。
