Theoretical Study On The Effect Of Hydrogen Bonding And Hydrogen Transfer On Sensitivity In Explosive

Hydrogen bonds and hydrogen transfer exist widely in hydrogen-contained explosives, and are of essential factors determining explosive structures, properties and performances. Therefore, it is an important breakthrough point for researching the structures and performances of explosives and their relationships. It is helpful to study the hydrogen bonds and hydrogen transfer to understand the complex mechanisms involved in the process of synthesis, preparation and the decomposition or detonation of explosives. In this thesis, we employed the hydrogen bonds and hydrogen transfer as a breakthrough point to study the mechanism of their effects on sensitivity against impact and thermal stimuli, using the quantum chemistry methods, crystal structure analysis tools and the reactive force field molecular dynamic (ReaxFF-MD) simulations.Firstly, we studied the effects of hydrogen bonds on the molecular interactions in the crystal, and acquired the mechanism of the hydrogen bonds effects on the impact sensitivity of explosives. We took a systemic analyses on the crystal packing of 11 existing low-sensitivity and high-energy explosives (LSHEs) whose both energy and safety close or superior to those of TNT, and 10 existing impact-sensitive high-energy explosives (SHEs) whose both velocities of detonation and impact sensitivity close to or higher than those of RDX. As a result, we found that each LSHEs molecule is π-bonded with a big conjugated structure composed of all non-hydrogen atoms in the entire molecule, and intramolecular hydrogen bonding exists in most LSHEs molecules resulting in high molecular stability. While intramolecular hydrogen bonding barely exists in SHEs, leading to their lower stability than LSHEs. The π-π stacking with the aid of intermolecular hydrogen bonds (HBs) is the main packing style of LSHEs crystals. However, it is lack in the SHEs crystals. We suggest that the planar conjugated molecular structures and intermolecular hydrogen bonding supporting the π-π tacking are necessary to the crystal engineering of LSHEs. Hydrogen bonding possesses the most percentage of the intermolecuar interactions of LSHEs crystals and the O…O interactions occupy the second place, while the O…O interactions dominate the interactions of SHEs, and per O…O interaction is usually weak so that SHEs are sensitive.Then, we took the model molecules and the applied explosive molecules as the objectives to study the intramolecular hydrogen transfer, which is influenced by the relative position of the transferred hydrogen atom to the nitro group, labeled as α,β and γ, and the environment of the molecule. As results, for α, the higher degree protonation of the transferred hydrogen (the higher charge of the hydrogen), the lower the reaction barrier; for β, it still follows the above trend of α; for y, the intramolecular hydrogen transfer reaction usually take place under excitated states. Besides, compared with another decomposition path initiating from the dissociation of C/N/O-NO2 bonds, the intramolecular hydrogen transfer in β and γ is more likely to occur in contrast to a.In addition, we studied the thermal decomposition mechanism of nitromethane (NM), dependent on temperature and density, to clarify the mechanism of the effects of intermolecular hydrogen transfer on thermal sensitivity of explosives. At 2000 K, the decomposition rate of NM is very slow; while at 2500 K, the bimolecular hydrogen transfer starts in the initial decomposition path at some high density. Above 2500 K, for example, till 3500 K, the initial decomposition mechanism of NM depends on density:the C-NO2 cleavage is the dominant route of the initial thermal decomposition when the density is lower than 1.71 g/cm3, while the dominant route switches to the intermolecular hydrogen transfer when density above 1.71 g/cm3.Summarily, we studied the characteristics of the hydrogen bonds in the LSHEs and SHEs crystals, the intramolecular hydrogen transfer of explosive molecules, and the thermal decomposition mechanism of NM dependented on temperature and density. These results are helpful to reveal the effects on the stability of the molecules, and the effects of the hydrogen bonds on the impact sensitivity of explosives and the effect of the hydrogen transfer on the thermal stability of explosives. On the basis of this study, we hope our results may be useful for designing new explosive molecules and the crystal engineering.