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.