Atomic Tunneling in Organic Reactions

为了阐明氢原子分子间和分子内隧穿的机理，用ESR、IR、MS和产物分析等手段研究了有机体系中氢原子在10~290K温度范围内的提取、加成和交换过程。结果如下：1)氢原子的量子力学隧穿是对低温化学反应的测量过程，因为反应体系的热激活概率与隧穿几率可以忽略不计。2)隧穿速率与隧穿势垒面积和隧穿粒子的有效质量成指数关系。这一速率强烈依赖于周围环境的粘度，如果在最佳隧穿过程中，不仅一个隧穿粒子需要形变，而且反应体系中的其他原子也需要形变。高粘度的环境防止OP…反应体系的变形更多的最大隧穿使得隧道势垒增加。3)氢原子的隧穿在宇宙化学中起着重要的作用。隧穿速率一般按抽提、加成双键、加成自由基的顺序递增。乙烷只是氢原子喷射到乙烯低温薄膜上的产物，因为氢原子加成产生的乙基与氢原子相继反应。氢原子加成的效率随着温度的降低而增加，这是因为氢原子扩散的减慢导致了隧穿反应时间的增加。4)卡宾和硝烯中氢原子分子内转移的隧穿势垒的形状强烈地依赖于电子构型和单态和三态之间的能量差。5)在BINAP/Ru催化的不对称氢化反应中，常温下氢原子的隧穿作用并不明显。较少

For elucidating the mechanism of inter- and intra-molecular tunneling of hydrogen atoms, hydrogen-atom abstraction, addition and exchange in organic systems have been studied between the temperature range of 10 K to 290 K by means of ESR, IR, mass spectroscopy, and product analyses. The results are summarized as follows ;1) Quantum-mechanical tunneling of hydrogen atoms is the measure process of chemical reaction at low temperatures, since the probability of the thermal activation of reaction systems is negligible with respect to the tunneling probability.2) The rate of tunneling depends exponentially on the area of tunneling barriers and the effective mass of tunneling particles. The rate strongly depends on the viscosity of the surroundings, if the deformation of, not only a tunneling particle, but also the other atoms in a reaction system are necessary during the optimum tunneling process. The surroundings with high viscosity prevent the deformation of the reaction-system for the op … More timum tunneling so that the tunneling barrier increases.3) The tunneling of hydrogen atoms plays a significant role in cosmic chemistry. The rate of the tunneling generally increases in the order of abstraction, addition to double bonds, and addition to free radicals. Ethane is only the product by hydrogen atom spray to the cryogenic thin film of ethylene, since the ethyl radicals generated by hydrogen-atom addition successively react with hydrogen atoms. The efficiency of the hydrogen-atom addition increases with decreasing temperature, since the slowing down of the diffusion of hydrogen atoms causes the increase of the reaction time for the tunneling.4) The shapes of the tunneling barriers for the intramolecular transfer of hydrogen atoms in carbene and nitrene strongly depend on the electronic configurations and the energy differences between the singlet and the triplet states.5) Hydrogen-atom tunneling does not play a significant role at ambient temperature in asymmetric syntheses by BINAP/Ru-catalyzed hydrogenation. Less