Assessment of ab initio MP2 and density functionals for characterizing the potential energy profiles of the SN2 reactions at N center.

The potential energy profiles of five selected bimolecular nucleophilic substitution (S(N) 2) reactions at nitrogen (N) center have been reinvestigated with the CCSD(T), G3[MP2,CCSD(T)], MP2, and some density functional methods. The basis sets of 6-31+G(d,p) and 6-311+G(3d,2p) are used for the MP2 and density functional calculations. Taking the relative energies at the CCSD(T)/CBS level of theory as benchmarks, we recommend the MP2, B97-K, B2K-PLYP, BMK, ωB97X-D, M06-2X, M05-2X, CAM-B3LYP, M08-SO, and ωB97X methods to generally characterize the potential energy profiles for the S(N)2 reactions at N center. Furthermore, these recommended methods with the relatively small 6-31+G(d,p) basis set may also be used to perform direct classical trajectory simulations to uncover the dynamic behaviors of the S(N)2 reactions at N center.