Eckhardt André K, Gerbig Dennis, Schreiner Peter R
Institute of Organic Chemistry, Justus-Liebig University , Heinrich-Buff-Ring 17, 35392 Giessen, Germany.
J Phys Chem A. 2018 Feb 8;122(5):1488-1495. doi: 10.1021/acs.jpca.7b12118. Epub 2018 Jan 30.
Although frequently employed, heavy atom kinetic isotope effects (KIE) have not been reported for quantum mechanical tunneling reactions. Here we examine the secondary KIE through C-substitution of the carbene atom in methylhydroxycarbene (HC-C̈-OH) in its [1,2]H-tunneling shift reaction to acetaldehyde (HC-CHO). Our study employs matrix-isolation IR spectroscopy in various inert gases and quantum chemical computations. Depending on the choice of the matrix host gas, the KIE varies within a range of 1.0 in xenon to 1.4 in neon. A KIE of 1.1 was computed using the Wentzel-Kramers-Brillouin (WKB) CVT/SCT, and instanton approaches for the gas phase at the B3LYP/cc-pVTZ level of theory. Computations with explicit consideration of the noble gas environment indicate that the surrounding atoms influence the tunneling reaction barrier height and width. The tunneling half-lives computed with the WKB approach are in good agreement with the experimental results in the different noble gases.
尽管重原子动力学同位素效应（KIE）经常被使用，但尚未见有关于量子力学隧穿反应的报道。在此，我们通过在甲基羟基卡宾（HC-C̈-OH）的[1,2]H隧穿转移反应生成乙醛（HC-CHO）过程中对卡宾原子进行碳取代来研究二级KIE。我们的研究采用了在各种惰性气体中的基质隔离红外光谱以及量子化学计算。根据基质主体气体的选择，KIE在氙气中的范围为1.0至氖气中的1.4之间变化。在理论水平为B3LYP/cc-pVTZ的气相中，使用温策尔-克拉默斯-布里渊（WKB）变分过渡态理论（CVT）/小曲率隧道效应（SCT）以及瞬子方法计算得到的KIE为1.1。明确考虑稀有气体环境的计算表明，周围原子会影响隧穿反应势垒的高度和宽度。用WKB方法计算得到的隧穿半衰期与在不同稀有气体中的实验结果吻合良好。
