Single solvent molecules can affect the dynamics of substitution reactions
Single solvent molecules can affect the dynamics of substitution reactions
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DOI：
10.1038/nchem.1362
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发表时间：
2012-07-01
期刊：
影响因子：
21.8
通讯作者：
Wester, R.
中科院分区：
文献类型：
--
作者：
Otto, R.;Brox, J.;Wester, R.
溶剂对溶液中的化学反应有着深远的影响，长期以来一直被用来控制化学反应的结果。这种效应通常被认为是由热力学控制的；然而，人们对溶剂分子的空间效应知之甚少。在这里，我们探讨了单个溶剂分子对反应动力学的影响，并给出了微溶剂化化学反应的原子动力学结果-最重要的亲核取代反应。我们使用交叉光束成像和冷源微溶剂化反应物相结合的技术研究OH-与CH3I的反应。我们的研究结果揭示了几种不同程度的溶剂化反应机制；令人惊讶的是，经典的共线性取代机制仅在单溶剂化反应物的动力学中占主导地位。我们使用从头计算分析了不同机制的相对重要性，并表明在理解这种微溶剂化反应中溶剂分子的影响时，位阻特征至少与能量学一样相关。
Solvents have a profound influence on chemical reactions in solution and have long been used to control their outcome. Such effects are generally considered to be governed by thermodynamics; however, little is known about the steric effects of solvent molecules. Here, we probe the influence of individual solvent molecules on reaction dynamics and present results on the atomistic dynamics of a microsolvated chemical reaction-the fundamentally important nucleophilic substitution reaction. We study the reaction of OH- with CH3I using a technique that combines crossed-beam imaging with a cold source of microsolvated reactants. Our results reveal several distinct reaction mechanisms for different degrees of solvation; surprisingly, the classical co-linear substitution mechanism only dominates the dynamics for mono-solvated reactants. We analyse the relative importance of the different mechanisms using ab initio calculations and show that the steric characteristics are at least as relevant as the energetics in understanding the influence of solvent molecules in such microsolvated reactions.