Structures and properties of the isomers of hexanitrosobenzene: A DFT study

Fourteen isomers of hexanitrosobenzene (HNOB) have been studied using the ab initio and density functional theory (DFT). Five stable isomers (1, 2, 10, 11 and 12) were found at the DFT-B3LYP level and the furazan structure 1 commonly called BTF has the lowest energy. The geometries, frequencies, and thermodynamic functions of the five stable isomers of HNOB and the ion of BTF have been calculated at the B3LYP/6-31G* level. Calculations have also been carried out on BTF at BLYP and MP2 levels with the 6-31G* basis set for comparison. Electron affinity of BTF was predicted to be 185.52 kJ/mol in gas phase at 298.15 K. Natural bonding orbital analysis was performed and the bonding condition of the stable isomers was described. The natural charges have been used to estimate the binding energies of 1s electrons of atoms in these isomers, and the calculated results of BTF were compared with the experimental results and were found to be satisfactory. The equilibrium contents of various stable isomers were estimated. 1 has the largest content (mole fraction is 0.29) and the contents of 10-12 are very close in magnitudes (0.22-0.23) and only slightly lower than that of 1, but the content of 2 is very low (0.02). The heats of formation of 1, 2, 10, 11 and 12 have been deduced from the two designed reactions, and the results are 489.53, 1570.04, 496.88, 515.67 and 507.68 kJ/mol, respectively. The possible reason for the change in the color of BTF upon exposure to light was given.