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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Hyperconjugation: The Electronic Mechanism That May Underlie the Karplus Curve of Vicinal NMR Indirect Spin Couplings
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Hyperconjugation: The Electronic Mechanism That May Underlie the Karplus Curve of Vicinal NMR Indirect Spin Couplings

机译：超共轭：电子机制可能是相邻的核磁共振间接自旋耦合的Karplus曲线的基础

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摘要

The electronic origin of the Karplus-type behavior of vicinal NMR J couplings for H^X-C^H.;-XH3,X= C,Sn model compound is analyzed within the framework of the polarization propagator formalism.It is shown that its whole pattern can be understood by generalizing previous hyperconjugative mechanisms,in such a way that the hyperconjugative delocalization effect from an excitation sigma->sigma~* should be replaced by two simultaneous excitations according to a second-order electronic property.All and the main coupling pathway which involve,at the random phase level of approach,RPA,the two pairs of localized MOs closest to the coupled nuclei follows a Karplus-type dependence with dihedralX-C-C-Xangle,theta.The specific two-electron integrals which include correlation at RPA level of approach are the main factors which define the total behavior of J.The Karplus-type dependence is also found at HF level for individual coupling pathways though that is not observed for the total J;the so-called nonlocal "perturbators" together with the inverse of the differences of energies define,at this level of approach,the functional dependence with theta.
机译：在极化传播子形式学的框架内分析了H ^ XC ^ H。;-XH3，X = C，Sn模型化合物的邻域NMR J偶合的Karplus型行为的电子起源。可以通过概括先前的超共轭机制来理解，即应根据二级电子性质用两个同时激发来代替激发sigma-> sigma〜*引起的超共轭离域作用。在接近随机相位RPA时，最靠近耦合核的两对局部MO遵循Karplus型依赖性，其二面角X-CC-Xangle，θ。特定的两电子积分包括RPA一级的相关性接近的方式是决定J整体行为的主要因素。虽然在总J中没有观察到，但在HF耦合水平的单个偶联途径中也发现了Karplus型依赖性;所谓的非局部的“扰动子”以及能量差的倒数，在这种方法的水平上，定义了与θ的函数依赖性。

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