College of Physics and Electronics, Shandong Normal University, Jinan 250014, People's Republic of China.
J Phys Chem A. 2011 Nov 3;115(43):12047-52. doi: 10.1021/jp2076808. Epub 2011 Oct 11.
The S(N)2 mechanism for the reaction of CH(3)Cl + OH(-) in aqueous solution was investigated using combined quantum mechanical and molecular mechanics methodology. We analyzed structures of reactant, transition, and product states along the reaction pathway. The free energy profile was calculated using the multilayered representation with the DFT and CCSD(T) level of theory for the quantum-mechanical description of the reactive region. Our results show that the aqueous environment has a significant impact on the reaction process. We find that solvation energy contribution raises the reaction barrier by ~18.9 kcal/mol and the reaction free energy by ~24.5 kcal/mol. The presence of the solvent also induces perturbations in the electronic structure of the solute leading to an increase of 3.5 kcal/mol for the reaction barrier and a decrease of 5.6 kcal/mol for the reaction free energy, respectively. Combining the results of two previous calculation results on CHCl(3) + OH(-) and CH(2)Cl(2) + OH(-) reactions in water, we demonstrate that increase in the chlorination of the methyl group (from CH(3)Cl to CHCl(3)) is accompanied by the decrease in the free energy reaction barrier, with the CH(3)Cl + OH(-) having the largest barrier among the three reactions.
采用量子力学和分子力学相结合的方法研究了 CH(3)Cl + OH(-)在水溶液中的 S(N)2 反应机制。我们沿着反应途径分析了反应物、过渡态和产物态的结构。使用多层表示方法，结合 DFT 和 CCSD(T)理论计算了反应自由能。结果表明，水相环境对反应过程有显著影响。我们发现溶剂化能贡献使反应势垒升高约 18.9 kcal/mol，反应自由能升高约 24.5 kcal/mol。溶剂的存在还会引起溶质电子结构的扰动，导致反应势垒增加 3.5 kcal/mol，反应自由能降低 5.6 kcal/mol。结合之前对 CHCl(3) + OH(-)和 CH(2)Cl(2) + OH(-)在水中反应的两个计算结果，我们证明了甲基氯化程度的增加（从 CH(3)Cl 到 CHCl(3)）伴随着反应自由能势垒的降低，而 CH(3)Cl + OH(-)的反应势垒在这三个反应中最大。
