Theoretical study of mechanism and dynamics on reaction of (CH3)2NH with CH3

The mechanism and dynamics for the bimolecular reaction of (CH3)2NH with CH3 have been investigated based on the G3//MP2/6-311G(d,p) level of theory. Our calculations show that when the two reactants approach each other, three prereaction complexes, RC1, RC2, and RC3, can be formed through van der Waals force or hydrogen bonding. From RC1, RC2, and RC3, six routes have been established. Among the six routes, the two routes (R1 and R2) from van der Waals prereaction complex RC1 are the main routes for the title reaction. R1 and R2 are hydrogen abstractions routes associated with HN and HCα atoms in DMA, respectively. The calculated energy barriers for R1 and R2 are 12.3 and 13.7 kcal/mol, respectively. Both the potential energy surfaces of R1 and R2 locate a "reactant-like" transition state, as well as van der Waals complexes before and after the transition state. The slight preference of R1 over R2 might be related to the higher similarity between the structures of RC1 and the transition state for R1 (TS1), namely, the structure of TS1 is more "reactant-like". The rate constants of the two favorable H abstraction reaction routes, R1 and R2, are evaluated over a wide temperature range of 200-3000 K by the variational transition state theory (VTST) methods, which can be expressed as kR1 = 5.30 × 10(-13)(T/1000)(3.0) exp(-2883/T) cm(3) molecule(-1) s(-1) and kR2 = 8.34 × 10(-13)(T/1000)(4.5) exp(-3100/T) cm(3) molecule(-1) s(-1), respectively. The predicted rate constant of the HN abstraction (route R1) is in good agreement with the available experimental data.