A dynamic prediction of stability for nitromethane in external electric field

Adding an external electric field into an energetic material system can increase the energy but the stability may be reduced.

A theoretical prediction of the possible trigger linkage of CH3NO2 and NH2NO2 in an external electric field

The effects of an external electric field on the C/N-NO2 bond with C/N-H and N-O bonds in CH3NO2 or NH2NO2 were compared using the DFT-B3LYP and MP2 methods with the 6-311++G(2d,p) and aug-cc-pVTZ basis sets. The results show that such fields have a minor effect on the C-N or C-H bond but a major effect on the N-O bond in CH3NO2, while in NH2NO2 electric fields affect the N-N bond greatly but the N-O or N-H bond only slightly. Thus, in CH3NO2, oxygen transfer or unimolecular isomerization to methyl nitrite might precede breaking of the C-N bond in the initial stages of decomposition, and the N-O bond could be the trigger bond in electric fields. In NH2NO2, however, N-N bond rupture may be preferential in an electric field and, consequently, the N-N bond might always be the real trigger bond. Atoms in molecules and natural bond orbital delocalization analyses, together with examination of shifts in electron density and frequencies support the above viewpoints. Forty-eight good linear correlations were found along the different field orientations at different levels of theory, including those between field strength (E) and changes in N-O/N-N bond length (ΔR N-O/N-N), ρ (N-O/N-N) values [Δρ (N-O/N-N), or stretching frequencies of the N-O/N-N bond (ΔυN-O/N-N). Graphical Abstract External electric fields have a major effect on the N-O or N-N bond inCH3NO2 or NH2NO2 , leading to a possible N-O trigger bond inCH3NO2 or a real N-N trigger bond in NH2NO2 in an electric field.

Sensitization of nitrocompounds by amines

A study has been carried out of the sensitization of nitromethane, trinitrotoluene, trinitrobenzene, picric acid and tetryl by the addition of small amounts of amines. The sensitization has been confirmed using dropweight impact experiments and a new method has been found, using differential scanning calorimetry, of making reproducible and quantitative measurements of the effect. It is found that the nitrocompound-amine mixtures decompose at temperatures lower than those of either of the pure components and show a drop in the impact energy required to cause initiation of ignition. The thermal decomposition experiments also yield substantially lower activation energies and an empirical sensitization factor (defined in the text) for nitromethane mixtures that decreases as the nitromethane aci-anion concentration increases. Kinetic deuterium isotope analysis points to C-N bond scission as the rate-determining step in the thermal decomposition of nitromethane and nitromethane-amine mixtures. Laser ionization mass analyses of the solid nitrocompound-amine mixtures indicate significant changes in the fragmentation patterns, with removal of the nitro-group occurring in all cases as the first step in the breakdown of the mixtures, which is not the case for the pure materials. Absorption bands appear in the UV / visible spectra of all the sensitized materials. These bands are ascribed to an intermolecular charge transfer from the nitrogen of an amine group to the antibonding orbital of the nitro-group. It is shown that, with small amounts of amines present, each amine molecule can form a complex with as many nitrocompound molecules as there are amine groups on it. The formation of this charge transfer complex is shown to weaken the nitrocompound C-N bond involved. The weakening of the C-N bond increases directly with increasing binding energy of the complex. Combined with the knowledge that the C-N bond breakage is the rate- ­determining step in the thermal decomposition of these materials and the suggestion that the dominant mechanism in their ignition/detonation is most likely thermal in origin, the sensitization is explained. This explanation deviates from the theories which have been previously proposed.