The potential energy profiles of F/OH-induced nucleophilic substitution (S_N2) and proton-transfer (PT) channels evolving with solvation for reactions of F^–(H₂O)_n=1–2 + CH₃I were characterized using B3LYP/ECP/d method. The hydrogen-bonded F^–(H₂O)_n---HCH₂I prereaction complex at the entrance of potential energy surface (PES) has a significant role on the reaction dynamics for each channel. Among the above three channels, the F-S_N2 channel is the most preferred and OH-S_N2 could be competitive. In contrast, the PT channel will occur at much higher collision energy. Importantly, for each channel, the central barrier is gradually increased with the addition of water molecules. This phenomenon indicates that the reactivity will decrease with degrees of solvation and this has been confirmed by experiment and direct dynamics simulations. Moreover, compared with the previous trajectory simulations, a non-IRC behavior has been uncovered. The water delivering process from fluorine to iodine side as illustrated on PES is barely observed, and instead, the reaction tends to dehydrate before passing through the S_N2 barrier and proceeds with the less hydrated pathway in order to weaken the steric effect. The work presented here shows the comprehensive potential energy surfaces and structures information on the F-S_N2, PT, and OH-S_N2 channels, and predict their competitive relationship, which would be helpful for better understanding the dynamics behavior of the title and analogous reactions.

中文翻译：

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F / OH诱导的S _N 2和质子转移反应与溶剂化反应的竞争

F / OH诱导的亲核取代（S _N 2）和质子转移（PT）通道随着溶剂化而演变为F ^–（H ₂ O）_{n = 1–2} + CH ₃ I反应的势能图B3LYP / ECP / d方法。的氢键合˚F ^-（H ₂ O）_Ñ --- HCH ₂我的预反应络合物在势能表面（PES）的入口处对反应动力学每个信道的显著作用。在上述三个频道中，FS _N 2频道是最优选的，OH-S _N2可能具有竞争力。相反，PT通道将以更高的碰撞能量发生。重要的是，对于每个通道，中央障碍物会随着水分子的添加而逐渐增加。该现象表明反应性将随着溶剂化程度的降低而降低，这已通过实验和直接动力学模拟得到证实。此外，与以前的轨迹模拟相比，已经发现了非IRC行为。几乎没有观察到PES所示的从氟到碘的水输送过程，相反，该反应倾向于在通过S _N之前脱水。2屏障，并以较少水合的途径进行，以减弱空间效应。此处介绍的工作显示了FS _N 2，PT和OH-S _N 2通道上的全面势能面和结构信息，并预测了它们之间的竞争关系，这将有助于更好地理解标题和类似物的动力学行为。反应。