Hybrid Quantum Mechanical/Molecular Mechanics Study of the SN2 Reaction of CH3Cl+OH- in Water

Journal Article · Thu Nov 03 04:00:00 EDT 2011 · Journal of Physical Chemistry A, 115(43):12047-12052

DOI:https://doi.org/10.1021/jp2076808· OSTI ID:1030475

Yin, Hongyun; Wang, Dunyou; Valiev, Marat

The SN2 mechanism for the reaction of CH3Cl + 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 multi-layered 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 CHCl3 + OH- and CH2Cl2 + OH- reactions in water, we demonstrate that increase in the chlorination of the methyl group (from CH3Cl to CHCl3) is accompanied by the decrease in the free energy reaction barrier, with the CH3Cl + OH- having the largest barrier among the three reactions.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1030475
• Report Number(s): PNNL-SA-82050; 34900; KC0301020
• Journal Information: Journal of Physical Chemistry A, 115(43):12047-12052, Journal Name: Journal of Physical Chemistry A, 115(43):12047-12052 Journal Issue: 43 Vol. 115
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AQUEOUS SOLUTIONS
CCSD(T)
CHLORINATION
DFT
ELECTRONIC STRUCTURE
Environmental Molecular Sciences Laboratory
FREE ENERGY
OH
SOLUTES
SOLVATION
SOLVENTS
WATER
ab-initio
aqueous-solution
calculations
chlorinated methanes
dynamics
electronic structure
gas-phase
ions
kinetics
minimum energy paths
molecular mechanics methodology
quantum
simulations