Theoretical investigation on structures, densities, detonation properties, and the pyrolysis mechanism of the derivatives of HNS.

The derivatives of 2,2',4,4',6,6'-hexanitrostilbene (HNS) are optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/6-31G* level. Detonation properties are evaluated using the modified Kamlet-Jacobs equations based on the calculated densities and heats of formation. It is found that there are good linear relationships between the density, detonation velocity, detonation pressure, and number of nitro, amino, and hydroxy groups. The thermal stability and pyrolysis mechanism of the title compounds are investigated by calculating the bond dissociation energies at the unrestricted B3LYP/6-31G* level. For the nitro and amino derivatives of HNS, the C-NO(2) bond is a trigger bond during the thermolysis initiation process, while for hydroxy derivatives, it is started from the isomerization reaction of the hydrogen transfer in the O-H bond. According to the quantitative standard of energetics and stability, as high-energy density compounds, 2,2',3,3',4,4',5,6,6'-nonanitrostilbene and 2,2',3,3',4,4',5,5',6,6'-decanitrostilbene essentially satisfy this requirement. In addition, we have discussed the effect of the nitro, amino, and hydroxy groups on the structure and properties.