High Energy Compounds Containing Pyridine Ring:Molecular Design And Theoretical Study

Theoretical methods such as density functional theory (DFT) have been used to study series of compounds containing the pyridine ring (nitramines, bridged dipyridines, pyridines incorporated with heterocycle rings) to predict their geometrical structures, electronic structures, detonation properties and crystal structures for screening the compounds with excellent performance for further investigations. The main contents are as following:1. Series of nitramines containing the pyridine ring were proposed to benefit from the insensitive characteristics of pyridine and high energy characteristics of nitramine and were investigated theoretically with DFT. The heats of formation (HOFs) were calculated with the PM3and DFT methods. The crystal density (p) was calculated with the volume obtained from the isodensity surface (Volume method) and that corrected with the electrostatic potential (Politzer method). Results of various methods were compared. The theoretical detonation energy (Q), detonation pressure (P), and detonation velocity (D) were evaluated with the Kamlet-Jacobs equations using the calculated p and HOF. Some compounds have high densities (ca.1.9g/cm3) and good performance (D>>9km/s, P>39GPa) and may be the potential candidates of high energy density compounds (HEDCs). The thermal stability and the pyrolysis mechanism of compounds were investigated by the predicted bond dissociation energies (BDE) and impact sensitivity (h50). Solvent effect has been investigated and it makes the studied compounds more stable in solutions. At last, the rules of molecular design of nitramines containing the pyridine ring were summarized.2. The-NO2、-NH2、-N3、-NHNO2、-ONO2、-CH2C(NO2) or-NF2derivatives of TNPyO (2,4,6-trinitropyridine N-oxide) and PYX (2,6-bis(picrylamino)-3,5-dinitropyridine) were designed and studied with DFT. The gas-phase HOFs were predicted based on the isodesmic reactions and the condensed-phase HOFs were estimated in the framework of the Politzer approach. The crystal densities were obtained via predicting the molecular packing using molecular mechanics (MM method). The detonation parameters (Q, D, P) were estimated. The effects of substituent groups on HOF, p, Q, D, and P were investigated. Sensitivity was evaluated using the frontier orbital energies, bond orders, BDEs and h50s. Considering the detonation performance and thermal stability, most of the TNPyO and some of the PYX derivatives are promising candidates of HEDC and worth further investigations.3. A set of dipyridines that have similar frameworks but different linkages (-O-,-NH--CH2-,-N=N-,-N=N(O)-,-CH=N-,-CH=CH-,-NH-NH or-NH-CH2-NH-) and substituents (-NH2,-N02or-NF2) were studied theoretically at the B3LYP/6-31G*level of DFT. The gas-phase HOFs were predicted based on the isodesmic reactions and the condensed-phase HOFs were estimated in the framework of the Politzer approach. The densities were obtained with three methods (Volume method, Politzer method, and MM method) and compared, and the MM method was found to be more reliable. The effects of different bridge groups on HOF were investigated. The predicted D and P indicate that compared with the directly linked dipyridines, the performance of dipyridines linked with-O-,-NH-, or-CH2-bridges has not been improved, while this is not the case for the dipyridines linked with the-N=N-,-N=N(O)-, and-NH-NH-bridge groups. The oxidation of pyridine N always but that of the-N=N-bridge does not always improve the detonation properties. The derivative with the-N=N-bridge and two-NF2substituent groups, has the largest D (9.90km/s) and P (47.47GPa). Analyses of the electronic structures show that the conjugation interaction exists between the bridge group and the pyridine ring. The stabilization effect of-NH-NH-and-NH-CH2-NH-is the largest, that of-CH=N-and-CH=CH-stands in the middle, and the effect of-N=N-and-N=N(O)-is the smallest. Analyses of BDEs show that all derivatives have good thermal stability.4. A set of derivatives of PRAN (2-(5-amino-3-nitro-1,2,4-triazolyl)-3,5-dinitropyridine) with different energetic substituents (-N3,-NO2,-NH2,-NF2) have been studied at the B3LYP/aug-cc-pvdz, B3LYP/6-31G(d), B3P86/6-31G(d), and B3PW91/6-31G(d,p) levels of density functional theory. The effects of different functionals and basis sets were analyzed.5. The MM method has been used to search for the most possible packing of new nitramine explosives Bis(1,3-dinitro-dihydro-lH-imidazo)[4,5-b:4’,5’-e]-4-nitropyridine (BNINP) and it’s N-oxide (BNiNPO) among the seven most possible space groups (P21/c, P-1, P212121, P21, C2/c, Pbca and Pna21) with the Dreiding and Compass force fields. Periodic ab initio calculations were performed on the predicted crystal structure using the GGA-PBE method of DFT. The thermodynamic functions of the obtained crystals I and II were evaluated. The crystal structures of another series of nitramines containing the pyridine ring have also been predicted with the MM method and optimized with the CA-PZ method of DFT. Analyses of the crystal energy gap indicate that four compounds are nearly conductors and other compounds are semiconductors. The largest contributions of atoms to the valence bands were analyzed.6. A new high energy compound NFP (7-Nitrotetrazolo[1,5]furazano[4,5-b] pyridine1-Oxide) was studied. The molecular geometrical and electronic properties, heat of formation and detonation properties were predicted. Crystal polymorphs of NFP were also predicted. Results compare well with experimental results. The calculated band gaps indicate the sensitivity of α-NFP is slightly lower than that of β-NFP. The effects of hydrostatic compression on the more stable α-NFP were investigated in the pressure range of0-100GPa.In summary, this dissertation has not only provided a large amount of basic data about high-energy pyridine compounds, but also summed up some valuable rules which are helpful for the further theoretical study and molecular design of the heterocyclic energetic materials.