Combined experimental and Computational Study on New Concept of Dynamics-Driven Organic Reaction and Path Bifurcation

采用全量子分子动力学(MD)方法，对取代的苄基甲酮肟和α-苯乙基甲酮肟在气相中的Beckmann反应进行了模拟。模拟结果表明，对于边界底物，反应路径发生了分叉，随着取代基的变化，反应产物由裂解变为重排。研究发现，分叉比与初始给予反应系统的能量有关。对取代基对反应速率和产物分布影响的物理有机实验表明，这些反应体系中存在路径分叉。基于最新发展的碎片分子轨道(FMO)-MD方法，利用自制的MD模拟应用程序对甲基重氮离子(CH3-N2)的水解反应进行了研究，该方法允许以全量子方式计算溶液动力学。模拟是使用一个水滴模型进行的，该模型由156个水分子组成，这些水分子包围着位于系统重心的底物(CH3-N2)。在一定的反应条件下，模拟成功地揭示了反应是如何发生的，以及反应分子和溶剂中的原子在从反应物状态到产物状态的反应过程中在分子水平上的行为。CH3-N2的水解通过SN2机制进行，因为通过C-N裂解形成的甲基阳离子太不稳定，不存在于亲核溶剂中，如水。模拟结果表明，CH3-N_2首先与C-H键中的一个水分子相互作用，然后H_2O与CH3部分相互作用取代N_2离开基团。O-C-N角从未像课本上写的那样达到180°。O-C键的形成和C-N键的断裂具有不同的同步性，表明溶液中化学反应的多样性。

Full quantum molecular dynamic(MD) simulations were carried out for the Beckmann reactions of substituted benzyl methyl ketone oximes and α-phenylethyl methyl ketoximes in the gas phase. The simulations revealed that reaction path bifurcation occurs for borderline substrates, where the reaction product changes from fragmentation to rearrangement with the change of substituent. The bifurcation ratios were found to have correlation with the amount of energy initially given to the reacting system. Physical organic experiment on the substituent effects on rates and product distribution suggests the existence of path bifurcation in these reaction systems.The hydrolysis reaction of methyl diazonium ion(CH3-N2+) was examined by means of home-made MD simulation application based on recently developed fragment molecular orbital(FMO)-MD method, which allows one to calculate solution dynamics in a full quantum fashion. The simulations were carried out by using a water droplet model consisting with 156 water molecules surrounding the substrate(CH3-N2+) located in the center of the gravity of the system. Under certain reaction conditions, the simulations succeeded to reveal how the reaction takes place and how the atoms in the reaction molecules and solvents behave during the reaction from the reactant state to the product state at the molecular level. The hydrolysis of CH3-N2+ proceeds via the SN2 mechanism since the methyl cation that would form via the C-N cleavage is too unstable to exist in nucleophilic solvent like water. The simulations showed that CH3-N2+ initial interacts with one of the water molecules in its C-H bond, and then H2O interacts with CH3 moiety displacing the N2 leaving group. The O-C-N angle never reached 180°as is written in the textbook. Variable synchronicity was observed for the O-C bond formation and the C-N bond cleavage, showing diversity in chemical reactions in solution.