微溶剂效应对 SN2 反应动力学的影响：直接 ab initio 轨线研究

The reaction dynamics in liquid phase have been an important subject. Solvents have profound influences on chemical reactions, whereas their effects remain largely unknown. Microsolvation offers an effective way to investigate the impact of solvent molecules on reaction dynamics. SN2 nucleophilic substitution reaction plays a vital role in organic chemistry and biochemistry, and has become a paradigmatic system for exploring the complicated dynamics because of its apparent simplicity and rich dynamical information. In this project, we plan to study the dynamics behaviors of typical microsolvated SN2 reactions X-(H2O)n + CH3I (X = F, Cl, OH; n = 1 – 3) by means of direct ab initio trajectory simulations. We also intend to extend the similar studies to X-(H2O) + CH3I(H2O) systems with the solvation of both reactants. It is expected that we will elaborate the characteristics and laws of these microsolvated SN2 reactions and reveal the reaction mechanisms on the atomic-level. Combined with gas phase dynamics and relevant experiments, we expect to reveal the role of solvent molecules on affecting and controlling the reactions, and hope to find new mechanisms. The findings will not only help to understand the dynamics of microsolvated SN2 reactions in detail, but also have important values in exploring solvent effects and more complicated reactions in solution.

液相反应动力学一直是化学研究领域的重要课题。溶剂对化学反应至关重要，但目前人们对溶剂效应的认识还很不够。微溶剂化为深入研究溶剂分子影响化学反应的动力学细节提供了有效手段。SN2亲核取代反应在有机和生物化学中占有重要地位，因其简单的形式和丰富的信息成为探索复杂反应动力学的模板。本项目将使用直接 ab initio 动力学方法对微溶剂化的典型 SN2 反应 X-(H2O)n + CH3I (X = F, Cl, OH; n = 1 – 3) 开展深入系统研究，也拟将类似研究扩展到两种反应物同时溶剂化体系 X-(H2O) + CH3I(H2O)。将在原子水平上阐明微溶剂化SN2反应的特征和规律，揭示微观反应机理。结合气相动力学和相关实验，探索溶剂分子对反应进程的影响和控制机制，可望发现新机理。研究结果不仅有助于深化对SN2微溶剂动力学的理解，而且对深入认识溶剂效应和复杂的液相反应具有重要的价值。

复杂的溶液环境对人们探索液相化学反应提出了挑战。微溶剂化提供了一种有效方式调查气相到液相化学反应的变化过程，深入认识溶剂效应。我们围绕该方向，对系列水化卤交换SN2反应开展了直接动力学研究，调查体系动力学性质和规律，理解水分子的影响和作用，揭示了反应的根本特征和微观反应机理。动力学计算获得了反应截面和产物能量分配等多种微观动力学信息，与实验结果吻合。模拟进一步阐明了水分子的稳定化和位阻效应、碰撞能、冲击参数等在反应动力学中的重要作用，解释了普遍观察到的在溶剂化SN2反应中低能溶剂化产物通道受到抑制的实验现象。研究结果可为在更深的层次上理解卤交换SN2反应机理，深入认识复杂的液相反应动力学和溶剂效应提供理论基础。