Molecular design and theoretical study of oxadiazole-bifurazan derivatives

CONTEXT

The design and synthesis of new high energy density materials is an important part of the research in the field of high energy materials. However, the synthesis of high-energy materials is very difficult and dangerous. Therefore, it is necessary to design the compounds in advance and evaluate the performance of the designed compounds, so as to screen the high-energy candidate compounds with excellent performance and provide reference for future synthesis and application. 1,2,5-oxadiazole (furazan) and 1,2,4-oxadiazole are five-membered nitrogen-oxygen heterocycles. Because their structures contain high-energy N-O, C=N bonds, they can effectively improve the energy density and oxygen balance of compounds, which has attracted widespread attention. In this paper, 42 kinds of oxadiazole-bifurazan energetic derivatives were designed by inserting different functional groups and changing the parent bridging groups with 1,2,4-oxadiazole and furazan as the basic structural units. Their electronic structures, aromaticity, heats of formation (HOFs), detonation properties, thermodynamic properties and electrostatic potential were systematically studied by density functional than theory (DFT). The results show that -C (NO₂)₃ has the greatest improvement effect on HOFs among all the substituent groups. The detonation performance of -N=N- bridged oxadiazole-bifurazan derivatives is better than that of -NH-NH- bridged derivatives. And -C(NO₂)₃ is the most effective group to improve the detonation performance and density of compounds. Compared with the parent compounds, when a -C(NO₂)₃ was introduced, the density increased by about 5.5%. A6 (D = 10.30 km·s^-1, P = 48.86 GPa) and D6 (D = 9.57 km·s^-1, P = 42.31 GPa) are the compounds with the best D and P among the designed compounds, which are higher than RDX and HMX, and are potential candidates for new high-energy materials.

METHODS

With the help of Gaussian16 software and Multiwfn 3.8 package, the B3LYP method in density functional theory was selected. The 6-311G (d, p) basis set was used to optimize the structure of the 42 derivatives, and the high-precision def2-TZVPP basis set was used to calculate the energy.

Combination multi-nitrogen with high heat of formation: theoretical studies on the performance of bridged 1,2,4,5-tetrazine derivatives

A series of bridged tetrazine derivatives (BDDT) were designed by using different bridges to connect two molecules of 1,2,4, 5-tetrazine oxides and then combining different substituents. At the same time, we used DFT-wB97/6-31 + G** method to regularly predict the HOMO-LUMO, heats of formation (HOF), detonation properties, thermal stability, and thermodynamic property orbitals of BDDT compounds. By studying the comprehensive relationship between different substituents and bridging and performance, it is shown that -N(NO₂)₂ and -C(NO₂)₃ are not only excellent groups to improve the heat of formation and detonation properties, but also can cause the compound to have a superior oxygen balance. And that the incorporation of the -N = N- and -NH-N = N- is helpful to enhance their thermal stabilities and HOF. -CH₂-CH₂- and -CH₂-NH- are good for improving the HOMO-LUMO energy gaps. Performances with positive HOF (1170-1590 kJ mol^-1), remarkable density (1.88-1.93 g cm^-3), outstanding detonation properties (D = 9.15-9.80 km s^-1, P = 38.24-44.40 GPa), and acceptable impact sensitivity lead C5, D8, E5, E7, F5, and F7 to be the potential candidates of HEDMs.

Predictive potential of eigenvalue-based topological molecular descriptors

This study is directed toward assessing the predictive potential of eigenvalue-based topological molecular descriptors. The graph energy, Estrada index, resolvent energy, and the Laplacian energy were tested as parameters for the prediction of boiling points, heats of formation, and octanol/water partition coefficients of alkanes. It was shown that an eigenvalue-based molecular descriptor cannot be individually used for successful prediction of these physico-chemical properties, but the first Zagreb index, the number of zeros in the spectrum and the number of methyl groups must be also involved in the models. Performed statistics show that the models constructed using the Estrada index and resolvent energy are significantly better than ones with the energy of a graph and the Laplacian energy. Such a trend is even more noticeable in the case of octanol/water partition coefficients of alkanes.

Characterizing structures, energetics, and spectra of species on the 1,3[H, C, As] potential energy surfaces: A high-level theoretical contribution

The ground and the low lying electronic states of structures on the ^1,3[H, C, As] potential energy surfaces were investigated with the highly correlated theoretical approaches CCSD(T), CCSD(T)-F12b, and CASSCF/MRCI along with the series of correlation consistent (aug-cc-pVnZ, n = D, T, Q, 5) basis sets. Energetic and spectroscopic parameters were obtained at the complete basis set limit, and the effect of core-valence correlation on these properties evaluated. Fundamental frequencies were also computed with the variational configuration interaction (VCI) approach. Heats of formation at 0 and 298.15 K were estimated for HCAs and CH, AsH, CAs, and HCAs, as well as the calculation of ionization potentials for HCAs. Comparisons of the present results with literature ones for the systems HCN/HNC, HCP/HPC highlight similarities and differences among these systems. Altogether, this investigation provides a very reliable characterization of the species on the surfaces and should guide future experimental studies on these systems.

DFT studies on nitrogen-rich pyrazino [2, 3-e] [1, 2, 3, 4] tetrazine-based high-energy density compounds

By using the density functional theory method, we investigated the heats of formation (HOFs), electronic structure, detonation properties, thermal stability and sensitivity for a set of pyrazino [2, 3-e] [1, 2, 3, 4] tetrazine derivatives with different substituents and different numbers of N-oxides. Our findings reveal that the HOFs of the derivatives decrease dramatically with the increasing number of N-oxides. The effects of the substituents on the HOMO-LUMO gaps are coupled with those of the N-oxides. The calculated detonation properties point out that -NF₂, -ONO₂ and an increasing number of N-oxides are very helpful for improving the detonation performance of the designed derivatives. The bond dissociation energies of the weakest bonds indicate that a majority of our designed compounds have better thermal stability. The -NH₂ group is very useful to decrease the free space value. Most of the derivatives have higher h₅₀ values compared with parent molecules. Considering the sensitivity, thermal stability and detonation performance, four compounds could be considered as potential candidates of high-energy density compounds.