Potential energy surface stationary points and dynamics of the F- + CH3I double inversion mechanism
Potential energy surface stationary points and dynamics of the F- + CH3I double inversion mechanism
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F-CH3I双反演机制的势能面驻点与动力学
DOI：
10.1039/c7cp02998e
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发表时间：
2017-08-14
影响因子：
3.3
通讯作者：
Hase, William L.
中科院分区：
文献类型：
--
作者：
Ma, Yong-Tao;Ma, Xinyou;Hase, William L.
采用直接动力学模拟方法研究了F- + CH 3 I反应中的S（N）2-DI双反转机理，并保留了构型.先前的模拟确定了S（N）2-DI机制的过渡态（TS）结构，即TS 0，包括反应路径。内禀反应坐标（IRC）计算表明，TS_0是一个质子转移（PT）TS，它与F-中心点中心点HCH_2 IS（N）_2反应前络合物和FH中心点CH_2 I质子转移后络合物相连。反应络合物因此，在S（N）2-DI机制中包含TS 0将涉及非IRC原子动力学。事实上，在TS 0开始的轨迹，具有RRKM理论假设的随机能量集合，优先形成S（N）2-DI产物，并且类似于70%遵循所提出的从TS 0到产物的S（N）2-DI途径。此外，突然矢量投影（SVP）方法被用来识别CH 3 I振动模式激发促进访问TS 0和S（N）2-DI机制。F- + CH 3 I模拟的结果，与SVP指定的模式激励，是令人失望的。当CH_3I的CH_3形变被激发时，S（N）_2单反转机制是主要的反应途径。如果CH伸缩模也被激发，质子转移占主导地位的反应。发生S（N）2-DI，但概率非常小，接近1%。这些结果背后的原因进行了讨论。
Direct dynamics simulations were performed to study the S(N)2 double inversion mechanism S(N)2-DI, with retention of configuration, for the F- + CH3I reaction. Previous simulations identified a transition state (TS) structure, i.e. TS0, for the S(N)2-DI mechanism, including a reaction path. However, intrinsic reaction coordinate (IRC) calculations from TS0 show it is a proton transfer (PT) TS connected to the F-center dot center dot center dot HCH2I S(N)2 pre-reaction complex and the FH center dot center dot center dot CH2I proton transfer post-reaction complex. Inclusion of TS0 in the S(N)2-DI mechanism would thus involve non-IRC atomistic dynamics. Indeed, trajectories initiated at TS0, with random ensembles of energies as assumed by RRKM theory, preferentially form the S(N)2-DI products and similar to 70% follow the proposed S(N)2-DI pathway from TS0 to the products. In addition, the Sudden Vector Projection (SVP) method was used to identify which CH3I vibrational mode excitations promote access to TS0 and the S(N)2-DI mechanism. Results of F- + CH3I simulations, with SVP specified mode excitations, are disappointing. With the CH3 deformations of CH3I excited, the S(N)2 single inversion mechanism is the dominant pathway. If the CH stretch modes are also excited, proton transfer dominates the reaction. S(N)2-DI occurs, but with a very small probability of similar to 1%. The reasons behind these results are discussed.