Showing papers by "Dunyou Wang published in 2012"

Hybrid Quantum Mechanical and Molecular Mechanics Study of the SN2 Reaction of CCl4+ OH-in Aqueous Solution: The Potential of Mean Force, Reaction Energetics, and Rate Constants

Abstract: The bimolecular nucleophilic substitution reaction of CCl4 and OH– in aqueous solution was investigated on the basis of a combined quantum mechanical and molecular mechanics method. A multilayered representation approach is employed to achieve high accuracy results at the CCSD(T) level of theory. The potential of mean force calculations at the DFT level and CCSD(T) level of theory yield reaction barrier heights of 22.7 and 27.9 kcal/mol, respectively. Both the solvation effects and the solvent-induced polarization effect have significant contributions to the reaction energetics, for example, the solvation effect raises the saddle point by 10.6 kcal/mol. The calculated rate constant coefficient is 8.6 × 10–28 cm3 molecule–1 s–1 at the standard state condition, which is about 17 orders magnitude smaller than that in the gas phase. Among the four chloromethanes (CH3Cl, CH2Cl2, CHCl3, and CCl4), CCl4 has the lowest free energy activation barrier for the reaction with OH– in aqueous solution, confirming the tr...

A multilayered-representation quantum mechanical/molecular mechanics study of the SN2 reaction of CH3Br + OH− in aqueous solution

Abstract: The bimolecular nucleophilic substitution (SN2) reaction of CH3Br 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 cm3 molecule−1 s−1 which agree very well with the experiment values at 23.0 kcal/mol and 2.6 × 10−25 cm3 molecule−1 s−1, respectively.