Mechanistic and kinetic study on the SN2 and E2 reactions of Cl− with CH3OBr

Dual-level direct dynamics method is employed to study the kinetics of the multiple-channel reaction CH3OBr + Cl− for the first time. Geometries have been optimized at the MP2 level with the 6-311+G(d,p) basis set. The minimum energy path is calculated at the same level and further refined at the QCISD(T)/6-311++G(3df,2p) level. The rate constants are obtained by using the canonical variational transition state theory incorporating small-curvature tunneling correction in the temperature range of 200–3000 K. The results show that anti-E2 elimination reaction channel is the dominant channel over the whole temperature range and the corresponding rate constants present negative temperature dependence in the low temperature range, while positive temperature dependence in the high temperature range. The three-parameter Arrhenius expression k = 2.61 × 10−18 T2.29 exp(1395.19/T) for the overall reaction is also given.