Computational details
The geometric parameters of all the reactants, transition states,
intermediates, and products involved in the proposed reaction mechanism
are optimized using M06-2X functional and 6-311+G* basis set. The
above-mentioned hybrid meta-generalized gradient-approximations (hybrid
meta-GGAs) M06-2X is recommended for studying thermochemistry, kinetics,
noncovalent interactions [20–23]. The
corresponding harmonic vibrational frequency calculations are performed
to identify the nature of stationary points on the potential energy
surface using the same level of theory [24]. The
local minima are confirmed with the real frequency in all reactants,
intermediates and product structures, whereas the corresponding
transition structure has only one imaginary frequency. Further, the
reaction path is calculated through intrinsic reaction coordinates
(IRCs) [25] to find the right transition states
which connect the two equilibrium structures [26].
To obtain more accurate relative energies, the single point energy is
carried out using CCSD (T) [27] functional and
6-311+G* level of theory. Thermodynamic properties enthalpy (ΔH),
entropy (ΔS) and Gibbs free energy (ΔG) are calculated by including a
thermodynamic correction to the potential energy surface at 298.15 K and
1 atmospheric pressure. All the electronic structure calculations are
performed using Gaussian 09 program package [28].
In this study, the kinetic rate constants are calculated by the
canonical variational transition (CVT) state theory[18] including small curvature tunneling
(SCT)[19] over the temperature range of 278-350 K
which are performed at M06-2X/6-311+G* level of theory.