Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, USA.
J Phys Chem A. 2009 Oct 29;113(43):11919-25. doi: 10.1021/jp903345x.
The rate constants of three intramolecular hydrogen-transfer isomerization reactions, namely, 1-4 isomerization of the 1-pentyl radical and 1-4 and 1-5 isomerizations of the 1-hexyl radical, are calculated using variational transition state theory with multidimensional tunneling, in particular by using canonical variational theory (CVT, which is the version of variational transition state theory in which the transition state dividing surface is optimized for a canonical ensemble) with small-curvature tunneling (SCT) for the transmission coefficient. The required potential energy surfaces were obtained implicitly by direct dynamics employing interpolated variational transition state theory with mapping (IVTST-M) and variational transition state theory with interpolated single-point energies (VTST-ISPE). Single-level direct dynamics calculations were performed for all of the reactions by IVTST-M using M06-2X/MG3S or M08-HX/cc-pVTZ+ potential energy surfaces or both. The stationary points of 1-4 isomerization of 1-pentyl and the stationary points for the forward reactions of 1-4 and 1-5 isomerizations of 1-hexyl were also optimized by BMC-CCSD, and for all three reactions we also performed dual-level direct dynamics calculations using VTST-ISPE in which MCG3-MPW single-point energies served as the higher level. The calculated MCG3-MPW//M06-2X/MG3S rate constants agree well with experimental values for 1-4 isomerization of the 1-pentyl radical at high temperature, and this validates the accuracy of this theoretical method for 1-4 isomerization. The MCG3-MPW//M06-2X/MG3S method was therefore used to make a reliable prediction for the rata constants of 1-4 isomerization of the 1-hexyl radical for which a direct experimental measurement is not available. The calculated CVT/SCT/M08-HX/cc-pVTZ+ rate constants agree well with experimental values for 1-5 isomerization of the 1-hexyl radical, and they show that the tunneling effect for these reactions was underestimated in previous work.
使用变分过渡态理论和多维隧道，特别是使用正则变分理论（CVT，即过渡态分割面针对正则系综进行优化的变分过渡态理论版本）和小曲率隧道（SCT）计算了三个分子内氢转移异构化反应的速率常数，即 1-戊基自由基的 1-4 异构化和 1-己基自由基的 1-4 和 1-5 异构化。所需的势能面通过直接动力学隐式获得，采用插值变分过渡态理论与映射（IVTST-M）和插值单点能量的变分过渡态理论（VTST-ISPE）。通过 IVTST-M 使用 M06-2X/MG3S 或 M08-HX/cc-pVTZ+势能面或两者的组合对所有反应进行了单水平直接动力学计算。通过 BMC-CCSD 优化了 1-戊基 1-4 异构化的驻点以及 1-己基 1-4 和 1-5 异构化的前向反应的驻点，对于所有三个反应，我们还使用 VTST-ISPE 进行了双水平直接动力学计算，其中 MCG3-MPW 单点能量作为较高水平。计算的 MCG3-MPW//M06-2X/MG3S 速率常数与高温下 1-戊基自由基 1-4 异构化的实验值吻合较好，这验证了该理论方法对于 1-4 异构化的准确性。因此，对于无法直接进行实验测量的 1-己基自由基 1-4 异构化，使用 MCG3-MPW//M06-2X/MG3S 方法进行了可靠的预测。计算的 CVT/SCT/M08-HX/cc-pVTZ+速率常数与 1-己基自由基 1-5 异构化的实验值吻合较好，表明这些反应的隧道效应在以前的工作中被低估了。
