Influence of Solvation and Dynamics on the Mechanism and Kinetics of Nucleophilic Aromatic Substitution Reactions in Liquid Ammonia

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• 作者：Samuel L. C. Moors ; Ben Brigou ; Dietmar Hertsen ; Balazs Pinter ; Paul Geerlings ; Veronique Van Speybroeck ; Saron Catak ; Frank De Proft
• 刊名：Journal of Organic Chemistry
• 出版年：2016
• 出版时间：February 19, 2016
• 年：2016
• 卷：81
• 期：4
• 页码：1635-1644
• 全文大小：652K
• ISSN：1520-6904

文摘

The role of the solvent and the influence of dynamics on the kinetics and mechanism of the S_NAr reaction of several halonitrobenzenes in liquid ammonia, using both static calculations and dynamic ab initio molecular dynamics simulations, are investigated. A combination of metadynamics and committor analysis methods reveals how this reaction can change from a concerted, one-step mechanism in gas phase to a stepwise pathway, involving a metastable Meisenheimer complex, in liquid ammonia. This clearly establishes, among others, the important role of the solvent and highlights the fact that accurately treating solvation is of crucial importance to correctly unravel the reaction mechanism. It is indeed shown that H-bond formation of the reacting NH₃ with the solvent drastically reduces the barrier of NH₃ addition. The halide elimination step, however, is greatly facilitated by proton transfer from the reacting NH₃ to the solvent. Furthermore, the free energy surface strongly depends on the halide substituent and the number of electron-withdrawing nitro substituents.