College of Physics and Electronics, Shandong Normal University, Jinan 250014, China.
J Chem Phys. 2012 Nov 14;137(18):184501. doi: 10.1063/1.4766357.
The bimolecular nucleophilic substitution (S(N)2) reaction of CH(3)Br and OH(-) in aqueous solution was investigated using a multilayered-representation quantum mechanical and molecular mechanics methodology. Reactant complex, transition state, and product complex are identified and characterized in aqueous solution. The potentials of mean force are computed under both the density function theory and coupled-cluster single double (triple) (CCSD(T)) levels of theory for the reaction region. The results show that the aqueous environment has a significant impact on the reaction process. The solvation effect and the polarization effect combined raise the activation barrier height by ~16.2 kcal/mol and the solvation effect is the dominant contribution to the potential of mean force. The CCSD(T)/MM representation presents a free energy activation barrier height of 22.8 kcal/mol and the rate constant at 298 K of 3.7 × 10(-25) cm(3) molecule(-1) s(-1) which agree very well with the experiment values at 23.0 kcal/mol and 2.6 × 10(-25) cm(3) molecule(-1) s(-1), respectively.
采用多层次表示的量子力学和分子力学方法研究了 CH(3)Br 和 OH(-)在水溶液中的双分子亲核取代(S(N)2)反应。在水溶液中鉴定并描述了反应物络合物、过渡态和产物络合物。在反应区域下，根据密度泛函理论和耦合簇单双(三)(CCSD(T))理论水平计算了平均力势。结果表明，水溶液环境对反应过程有显著影响。溶剂化效应和极化效应共同使活化能垒升高约 16.2 kcal/mol，其中溶剂化效应是平均力势的主要贡献。CCSD(T)/MM 表示的自由能活化能垒为 22.8 kcal/mol，298 K 时的速率常数为 3.7×10(-25)cm(3)分子(-1)s(-1)，与实验值在 23.0 kcal/mol 和 2.6×10(-25)cm(3)分子(-1)s(-1)分别非常吻合。
