Chemical Kinetics for Reaction of 5-Nitro-1H-benzo[d]imidazole to Produce 6-Nitro-1H-benzo[d]imidazole and Calculation of Heat Capacity of Activation

The kinetics and mechanism of the reaction of 5-nitro-1H-benzo[d] imidazole to produce 6-nitro-1H-benzo[d] imidazole was studied by employing hybrid meta-density functional theory. MPWBlK/6-31+G** level calculations were carried out to obtain energies and optimize the geometries of all stationary points along the PES, and determine the harmonic vibrational frequencies. Two transition states (TS1 and TS2) and a chemically-energized intermediate (Int) are involved along the calculated potential energy surface. RRKM-TST was used to compute the temperature dependence of the rate constants, which were determined using nonlinear least-squares fitting at 273-1000 K. The Arrhenius plot for all reactions was shown positive temperature dependence. Thermodynamic parameters were also used to determine the stability and the extent of spontaneity of the reaction. The self-consistent reaction field (SCRF) was used with DFT energy, optimization, and frequency calculations to model systems in solution and compare them with the rate constants in the gas and solvent (water) phases. The variation of activation energy in the temperature range (273-1000 K) were determined in the gas and solvent phases. The heat capacity of activation of reactions ((∂E_a)/∂T) were also reported which is temperature dependent and is significant in low temperature.