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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Ab Initio Tests of the Marcus Equation for the Prediction of the Position of the Transition State for the Reaction H + C↓(2)H↓(5)R→CH↓(4) + CH↓(2)R with R = H, CH↓(3), NH↓(2), CN, CF↓(3), and C↓(6)H↓(5)
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Ab Initio Tests of the Marcus Equation for the Prediction of the Position of the Transition State for the Reaction H + C↓(2)H↓(5)R→CH↓(4) + CH↓(2)R with R = H, CH↓(3), NH↓(2), CN, CF↓(3), and C↓(6)H↓(5)

机译：预测反应H + C↓（2）H↓（5）R→CH↓（4）+ CH↓（2）R（其中R = H）的Marcus方程从头算的预测过渡态位置，CH↓（3），NH↓（2），CN，CF↓（3）和C↓（6）H↓（5）

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摘要

Marcus originally derived the Marcus equation to predict Br#nsted coefficients for electron-transfer reactions. However in the literature it is often assumed that Marcus' result can be extended to predict positions of the transition state for atom-transfer reactions. In this paper we use ab initio methods to examine the potential energy surface and transition state of a series of hydrogenolysis reactions of the form H·+ CH↓(3)CH↓(2)R→CH↓(4) +·CH↓(2)R, with R = H, CH↓(3), CF↓(3), CN, NH250L?2), and C↓(5)H↓(6), in order to see if the Marcus equation can be extended to atom-transfer reactions. The calculations show that the molecular orbitals of the system look "reactant-like" moving up the potential energy surface toward the transition state, and then switch to "product-like" moving down to products, in qualitative agreement with what one would expect from the Marcus equation. However, the curve crossing from "reactant-like" to "product-like" molecular orbitals does not occur at the saddle point in the potential energy surface. Rather the curve crossing occurs at a point part way down to products. Also most of the barrier to reaction is associated with rearrangements of the electron clouds due to Pauli repulsions when the reactants come together and not with the bond destruction and bond formation processes. These rearrangements are not considered in the Marcus equation. We do not yet know if our results are special to the reactions here or are general. However, it does appear that some key physics is missing when one extends the Marcus model to atom- or ligand-transfer reactions. One can represent the key physics with a modified bond additivity potential, however.
机译：Marcus最初导出了Marcus方程，以预测电子转移反应的Br＃nsted系数。然而，在文献中通常假设马库斯的结果可以扩展为预测原子转移反应的过渡态位置。在本文中，我们使用从头算的方法检查了一系列氢解反应的势能面和跃迁状态，这些形式为H·+ CH↓（3）CH↓（2）R→CH↓（4）+·CH↓ （2）R，其中R = H，CH↓（3），CF↓（3），CN，NH250L？2）和C↓（5）H↓（6），以便查看Marcus是否该方程可以扩展到原子转移反应。计算表明，该系统的分子轨道看起来像“反应物样”，沿着势能表面向上移动到过渡态，然后切换为“产品样”，向下移动到产品，这与人们的预期定性一致。马库斯方程式。但是，从“类似反应物”到“类似产物”的分子轨道的曲线在势能表面的鞍点处不会出现。相反，曲线交叉发生在部分下降到产品的点上。同样，大多数反应障碍与电子云的重排有关，这是由于当反应物聚集在一起时由于泡利的排斥，而不是与键破坏和键形成过程无关。在Marcus方程中不考虑这些重排。我们尚不知道我们的结果对这里的反应是特殊的还是普遍的。但是，当人们将Marcus模型扩展到原子转移或配体转移反应时，确实缺少了一些关键的物理方法。但是，可以用改进的键加性来表示关键物理。

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