Adlhart Christian, Uggerud Einar
Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, Oslo N-0315, Norway.
Phys Chem Chem Phys. 2006 Mar 7;8(9):1066-71. doi: 10.1039/b516658f. Epub 2006 Jan 10.
Despite the fact that the transition structure of the gas phase S(N)2 reaction H(2)O + HOOH(2)(+)--> HOOH(2)(+)+ H(2)O is well below the reactants in potential energy, the reaction has not yet been observed by experiment. Variational transition state RRKM theory reveals a strong preference for the competing proton transfer reaction H(2)O + HOOH(2)(+)--> H(3)O(+)+ HOOH due to entropy factors. Born-Oppenheimer reaction dynamics simulations confirm these results. However, by increasing the collision energy to around 7.5 eV the probability for nucleophilic substitution increases relative to proton transfer. These observations are explained by the presence of the key common intermediate HOO(H)[dot dot dot]H-OH(2)(+) which leads to effective proton transfer, but can be avoided with increasing collision energy. However, the S(N)2 probability remains below 0.2 since successful passage through the TS requires optimum initial orientation of the reactants, excitation of the relative translational motion and good phase correlation between the O-O vibration and the motion of the incoming water.
尽管气相S(N)2反应H(2)O + HOOH(2)(+)--> HOOH(2)(+)+ H(2)O的过渡结构在势能上远低于反应物，但该反应尚未被实验观测到。变分过渡态RRKM理论表明，由于熵因素，竞争的质子转移反应H(2)O + HOOH(2)(+)--> H(3)O(+)+ HOOH具有很强的优势。玻恩-奥本海默反应动力学模拟证实了这些结果。然而，通过将碰撞能量增加到约7.5电子伏特，亲核取代的概率相对于质子转移增加。这些观测结果可以通过关键的共同中间体HOO(H)[dot dot dot]H-OH(2)(+)的存在来解释，它会导致有效的质子转移，但随着碰撞能量的增加可以避免。然而，S(N)2的概率仍低于0.2，因为成功通过过渡态需要反应物的最佳初始取向、相对平动的激发以及O-O振动与进入的水的运动之间良好的相位相关性。
