Meisner Jan, Markmeyer Max N, Bohner Matthias U, Kästner Johannes
Institute for Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, Stuttgart, Germany.
Phys Chem Chem Phys. 2017 Aug 30;19(34):23085-23094. doi: 10.1039/c7cp03722h.
Atom tunneling in the hydrogen atom transfer reaction of the 2,4,6-tri-tert-butylphenyl radical to 3,5-di-tert-butylneophyl, which has a short but strongly curved reaction path, was investigated using instanton theory. We found the tunneling path to deviate qualitatively from the classical intrinsic reaction coordinate, the steepest-descent path in mass-weighted Cartesian coordinates. To perform that comparison, we implemented a new variant of the predictor-corrector algorithm for the calculation of the intrinsic reaction coordinate. We used the reaction force analysis method as a means to decompose the reaction barrier into structural and electronic components. Due to the narrow energy barrier, atom tunneling is important in the abovementioned reaction, even above room temperature. Our calculated rate constants between 350 K and 100 K agree well with experimental values. We found a H/D kinetic isotope effect of almost 10 at 100 K. Tunneling dominates the protium transfer below 400 K and the deuterium transfer below 300 K. We compared the lengths of the tunneling path and the classical path for the hydrogen atom transfer in the reaction HCl + Cl and quantified the corner cutting in this reaction. At low temperature, the tunneling path is about 40% shorter than the classical path.
利用瞬子理论研究了2,4,6-三叔丁基苯基自由基与3,5-二叔丁基新戊基之间氢原子转移反应中的原子隧穿，该反应具有短而强烈弯曲的反应路径。我们发现隧穿路径在质量加权笛卡尔坐标中定性地偏离了经典本征反应坐标，即最速下降路径。为了进行这种比较，我们实现了一种预测-校正算法的新变体来计算本征反应坐标。我们使用反应力分析方法将反应势垒分解为结构和电子成分。由于能垒狭窄，原子隧穿在上述反应中很重要，甚至在室温以上也是如此。我们计算的350 K至100 K之间的速率常数与实验值吻合良好。我们发现在100 K时氢/氘动力学同位素效应接近10。在400 K以下，隧穿主导了氢的转移，在300 K以下，隧穿主导了氘的转移。我们比较了HCl + Cl反应中氢原子转移的隧穿路径和经典路径的长度，并量化了该反应中的拐角切割。在低温下，隧穿路径比经典路径短约40%。
