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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Direct-dynamics VTST study of the [1,7] hydrogen shift in 7-methylocta-1,3(Z),5(Z)-triene. A model system for the hydrogen transfer reaction in previtamin D-3
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Direct-dynamics VTST study of the [1,7] hydrogen shift in 7-methylocta-1,3(Z),5(Z)-triene. A model system for the hydrogen transfer reaction in previtamin D-3

机译：直接动力学VTST研究7-甲基辛基-1,3（Z），5（Z）-三烯中的[1,7]氢位移。维生素D-3中氢转移反应的模型系统

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Direct-dynamics canonical variational transition-state theory calculations with microcanonically optimized multidimensional transmission coefficient (CVT/mu OMT) for tunneling were carried out at the MPWB1K/6-31+G(d,p) level to study the [1,7] sigmatropic hydrogen rearrangement in 7-methylocta-1,3(Z),5(Z)-triene. This compound has seven conformers, of which only one leads to products, although all of them have to be included in the theoretical treatment. The calculated CVT/mu OMT rate constants are in good agreement with the available experimental data. To try to understand the role of tunneling in the hydrogen shift reaction, we have also calculated the thermal rate constants for the monodeuterated compound in the interval T = 333.2-388.2 K. This allowed us to evaluate primary kinetic isotope effects (KIEs) and make a direct comparison with the experiment. Our calculations show that both the large measured KIE and the large measured difference in the activation energies between the deuterated and root compounds are due to the quantum tunneling. The tunneling contribution to the KIE becomes noticeable only when the coupling between the reaction coordinate and the transverse modes is taken into account. Our results confirm previous experimental and theoretical works, which guessed that the obtained kinetic parameters pointed to a reaction with an important contribution due to tunneling. The above conclusion would be essentially valid for the case of the [1,7] hydrogen shift in previtamin D-3 because of the similarity to the studied model system.
机译：在MPWB1K / 6-31 + G（d，p）级别进行了微动力学优化的多维隧穿传输系数（CVT / mu OMT）的直接动力学规范变分过渡态理论计算，以研究[1,7] 7-甲基辛基-1,3（Z），5（Z）-三烯中的σ氢重排该化合物具有七个构象异构体，尽管在理论处理中必须将所有这些构象异构体引入其中，但只有一个会生成产物。计算出的CVT /μOMT速率常数与可用的实验数据非常吻合。为了试图了解隧穿在氢转化反应中的作用，我们还计算了在T = 333.2-388.2 K区间内单氘代化合物的热速率常数。这使我们能够评估主要的动力学同位素效应（KIEs）并得出与实验直接比较。我们的计算表明，氘代化合物和根化合物之间的大的实测KIE和大的实测活化能差都归因于量子隧穿。仅当考虑到反应坐标和横向模态之间的耦合时，对KIE的隧穿作用才变得明显。我们的结果证实了先前的实验和理论工作，他们猜测所获得的动力学参数指出了由于隧穿而起重要作用的反应。由于与所研究的模型系统相似，上述结论对于维生素原D-3中[1,7]氢转移的情况基本上是有效的。

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