Theoretical Study Of Substituent Effect On High Energetic Density Materials

The present dissertation is devoted to research on the structures and properties for a series of the compounds including difluoroamino, nitrato, nitor and azido groups, by using quantum mechanics (QM) and computational chemistry methods. We concentrated on "gas" molecular design for HEDM. Based on the QM calculations, the quantitative criteria of detonation performance as a HEDC (density p≈1.9 g/cm3, detonation velocity D≈9.0 km/s, and detonation pressure P≈40.0 GPa) and the stability are employed to recommend dozens of potential HEDM objectives from the title compounds. The title compounds include neopentyl difuoroamino compounds, four-membered ring compounds, piperidine and diazocine compounds and cubane derivatives.The heats of formation (HOFs) were calculated for a series of neopentyl difluoroamino compounds by using density functional theory (DFT) method with 6-311G** basis set, as well as semi-empirical methods. In the isodesmic reactions designed for the computation of HOF, the neopentane was chosen as a reference compound. The HOFs increase smoothly as -ONO2 groups being replaced by -NF2 and -NO2. However, HOFs increase dramatically as -ONO2 groups being replaced by -N(NO2)CH3 and -N3 groups. The variations of HOFs are different with different substituents. The semi-empirical MO (MNDO, AM1, and PM3) methods did not produce accurate and reliable results for the HOFs of the title compounds. The relative stability of the title compounds was evaluated based on the calculated HOFs, the energy gaps between the frontier orbitals and the bond order of C-R bond (C-NF2, C-ONO2, C-NO2 and C-N3). The magnitudes of intramolecular group interactions were predicted through the disproportionation energies. Thermal stabilities were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G** level. These results provide basic information for the molecular design of novel high energetic density materials.Density functional theory (DFT) method has been employed to study the geometric and electronic structures of a series of four-membered ring compounds including difluoroamino, nitrato, nitor and azido at the B3LYP/6-311G** and the B3P86/6-311G** levels. In the isodesmic reactions designed for the computation of heats of formation (HOFs),3,3-dimethyl-oxetane, azetidine, and cyclobutane were chosen as reference compounds. The HOFs for N3 substituted derivations are larger than those of oxetane compounds with ONO2 and/or NF2 substituent groups. The HOFs for oxetane with ONO2 and/or NF2 substituent groups are negative, while the HOFs for N3 substituted derivations are positive. For azetidine compounds, the substituent groups within the azetidine ring affect the HOFs. The values of HOFs increase as the difluoroamino group being replaced by the nitro group. The magnitudes of intramolecular group interactions were predicted through the disproportionation energies. The strain energy (SE) for the title compounds has been calculated using homodesmotic reactions. For azetidine compounds, the NF2 group connecting with the N atom in the ring decreases the SE of the title compounds. Thermal stability were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G** level. For the oxetane compounds, the O-NO2 bond is easier to break than the ring C-C bond. For the azetidine and cyclobutane compounds, the homolysises of C-NX2 and/or N-NX2 (X= O, F) bonds are primary step for bond dissociation. Detonation properties of the title compounds were evaluated by using the Kamlet-Jacobs equation based on the calculated densities and HOFs. 1,1-dinitro-3,3-bis(difluoroamino)-cyclobutane, with predicted density of ca.1.9 g/cm3, detonation velocity (D) over 9 km/s, and detonation pressure (P) of 41 GPa that are lager than those of TNAZ, is expected to be a novel candidate of high energy density materials (HEDMs). The detonation data of nitro-BDFAA and TNCB are also close to the requirements for HEDMs.Density functional theory calculations at the B3LYP/6-311G** level were performed to predict the heats of formation (HOFs) for three eight-membered ring compounds and four six-membered ring compounds via designed isodesmic reactions. The structures of title compounds are similar to those of RDX and HMX. The HOFs for -NO2 substituted derivations are larger than those of -NF2 substituent groups. Thermal stability were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G** level. As a whole, the homolysis of C-NF2 or C-NO2 bonds is the main step for bond dissociation of the title compounds. Detonation properties of seven title compounds were evaluated by using the Kamlet-Jacobs equation based on the calculated densities and HOFs. It is found that 3,3,7,7-tetrakis(difluoroamino)octahydro-1,5-dinitro-1,5-diazocine (HNFX) and 3,3,5,5-tetrakis (difluoroamino)-1-nitro piperidine (Nnitro TDFAPP), with predicted density of ca. 2.0 g/cm3, detonation velocity (D) about 9.9 km/s, and detonation pressure (P) of 47GPa that are lager than those of HMX, are expected to be the novel candidates of high energy density materials (HEDMs). The detonation data of 1,3,3,5,7,7-hexanitro-1,5-diazacyclooctane (HNDZ) and TNBDFAPP show that they meet the requirements for HEDMs.Strain is an important concept in structural organic chemistry. Homodesmotic reaction and isodesmotic reaction were designed for the computation of strain energies (SE) for a series of cubane derivatives. Total energies of the optimized geometric structures at the DFT-B3LYP/6-31G* level were used to derive the SE. The SE value of cubane is 169.13 kcal/mol via homodesmotic reaction, which is in good agreement with the experimental value. The variation of SE with respect to the number of substituents is similar for the homodesmotic reaction and isodesmotic reaction. The SE values of polynitrocubane and polydifluoroaminocubane increase slightly as up to four substituent groups being added to the cage skeleton. On contrary, the SE dramatically increases when the number of substituent groups m increases from 5 up to 8. For polynitratocubane, the SE decreases slightly at the beginning then increases as the number of group increases. For polyazidocubane, there are very small group effects on the SE. Among four types of substituent groups, the nitro group has greatest effect on the strain energy of caged cubane skeleton. The calculated SE value of octanitrocubane is 257.20 kcal/mol, while that of octaazidocubane is 166.48 kcal/mol obtained. The azido group releases the strain energy of cubane skeleton when the number of azido groups is less than 7. The interactions among the substituted groups deviated from group additivity. The substituted groups withdraw electrons from the cubane, reducing the repulsion between C-C bonds and resulting in the release the strain of the skeleton for isomers with fewer substituents. Group repulsions increase sharply with more and more nitro, nitrato and difluoroamino groups being attached to cubane, resulting large strains of the skeleton. The average negative charges of the substituted groups influence the strain energy of cubane derivatives.Density functional theory calculations at the B3LYP/6-311G** level was performed to predict the heats of formation (HOFs) for two pyrazine derivatives and six pyridine derivatives via designing the isodesmic reactions. The HOF value of LLM-105 is 28.28 kJ/mol. The N-oxidations for the ring nitrogen of pyrazine and pyridine derivatives decrease the HOF values compared to the parent compounds except TNPy and TNPyOx. Adding NH2 group can decrease the HOF value of title compounds; adding NO2 group can increase the HOF value of title compounds. Thermal stability were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G** level. The homolysise of C-NO2 bonds is the main step for bond dissociation of the title compounds. The position of groups influences the BDE values of C-NO2 and C-NH2 bond. The ortho-position groups relative to the heterocyclic N atom are easier to break than the same type of para-position groups.Homodesmotic reaction was designed for the computation of strain energies (SE) for four nitro substituted 1,3,5,7-tetraazacubane derivatives. Total energies of the optimized geometric structures at the DFT-B3LYP/6-31G* and DFT-B3LYP/6-311G** levels were used to derive the SE. The variation of SE with respect to the number of substituents is similar with both basis sets. The SE value is 237.32 kcal/mol at the B3LYP/6-311G** level for 2,4,6,8-tetranitro-1,3,5,7-tetraazacubane, which is unexpectedly much larger than that of its cubane analogue. The SE increases remarkably with more nitro groups being attached to the cage skeleton of tetraazacubane. The 'bending' of the bonds within the cubic skeleton attributes to the increase of strains as the attached number of nitro groups increases.In a word, the group effects and group interactions were investigated by designing rational isodesmic reactions. The performances for HEDM were judged quantitatively by criteria of energy and stability. Dozens of potential HEDM candidates were recommended among various series of neopentyl difuoroamino compounds, four-membered ring compounds, piperidine and diazocine compounds and cubane derivatives based on their performances. The physical, chemical characteristics and explosive properties, with the variations of subtituent group types, numbers and position, were obtained. These studies are innovative in the field of cross-disciplinary research of HEDC/HEDM.