Theoretical study on pyrolysis and sensitivity of energetic compounds

UHF–SCF–AM1 MO method has been applied to study pyrolysis initiation reactions (homolysis of bond C–NO2 into radicals) of seven nitro derivatives of aminobenzenes. Their potential energy curves and activation energies have been obtained first. The molecular geometries of the reactants, transition states and products of the seven reactions were fully optimized. It has been found that there is a parallel relationship between impact sensitivity, bond order (BC–N) of the weakest C–NO2 bond and activation energy (Ea) of the pyrolysis initiation reaction breaking this bond. Especially, good linear relationship exists between Ea and BC–N with a correlation coefficient of 0.985, showing that Ea and BC–N can both assess the relative magnitudes of impact sensitivity of this category of compounds. The result gives `the principle of the smallest bond order' (PSBO) a powerful support. Meanwhile, the stabilizing effect of the amino group and the sensitizing effect of the nitro group have been elucidated based on the calculation results of the heat of formation and the bond order of the initiation bond C–NO2.