Theoretical exploration of the stabilities and detonation parameters of nitro-substituted 1H-benzotriazole.

CONTEXT: The nitro group was introduced into the nitrogen heterocycle of 1H-benzotriazole to design a total of 31 derivatives. To estimate the thermal stability of these derivatives, the heat of formation (HOF) is calculated based on the isodesmic reaction. The bond dissociation energy (BDE) was also predicted based on the homolytic reaction to further evaluate the dynamic stability. To evaluate the possibility of utilizing as high energy density compounds (HEDCs), the detonation parameters including the detonation pressure (P), detonation velocity (D), and explosive heat (Q) are predicted by taking advantage of the Kamlet-Jacobs empirical equation. To measure the sensitivity to impact, both the characteristic height (H50) and free space in crystal (∆V) are considered in this paper. Based on our calculations, D-series and E are found to be the candidates for HEDCs. METHODS: The Gaussian 09 software package was used in this paper. The B3PW91 hybrid function with the 6-311 + G(d,p) basis set was chosen to perform the structural optimization, frequency analysis, heat of formation, and bond dissociation energy. The detonation parameters were calculated following the Kamlet-Jacobs equation.

CAS Calculation of the Excited States of the Methylthio Neutral Radical and Its Ions.

The complete active space (CASSCF) and the multiconfiguration second-order perturbation theory (CASPT2) calculations with 6-311++G(3df,3pd) gauss basis sets are performed for several electronic states of the methylthio neutral radical and its cation and anion. Twenty-two electronic states are optimized in the C s point group. Through the vertical promotion calculations, the absorption spectral is simulated for the neutral radical. Furthermore, through the energy comparison between the neutral radical and relative ions, the ionization energy and the electronic absorption energy are understood adiabatically.

Computational study about the thermal stability and the detonation performance of nitro-substituted thymine.

By replacing hydrogen atoms in thymine molecules with nitro groups, a series of new high-energy-density molecules are designed. To explore the thermal stability, the heats of formation (HOF) are calculated at the B3PW91-D3/6-311++G(2df,2p) level. The bond dissociation energy and the bond order are also calculated to predict the kinetic stability at the same level. Based on our calculations, excellent stability is confirmed for title molecules. To confirm the possibility of application as high-energy-density compounds, the molecular density (ρ), explosive heats (Q), detonation velocity (D), detonation pressure (P), free space per molecule in crystal lattice (ΔV), and characteristic drop height (H50) are calculated. On the consideration of the stability and the detonation characters, E1 is confirmed as the candidates of high-energy-density compounds.

Theoretical exploration about the thermal stability and detonation properties of nitro-substituted hypoxanthine.

Nitro-substituted derivatives of hypoxanthine are designed by substituting the hydrogen atoms by nitro groups. The heats of formation (HOF) are calculated at the G3MP2 level to confirm the thermal stability. Also, the bond dissociation energy (BDE) accompanied by the bond order is calculated at the same level to explore kinetic stability. To evaluate the potential application as high-energy density materials, the explosive heat, the molecular density, the detonation pressure, and detonation velocity are estimated by using the Kamlet-Jacobs (K-J) equation. Furthermore, the molecular sensitivities are considered by calculating the character height (H50) and the amount of free space per molecule in the crystal lattice (ΔV). Based on our calculations, the trinitro-substituted hypoxanthine (C) is screened out as the potential high-energy density compounds for further study.

Theoretical exploration about nitro-substituted derivatives of pyrimidine as high-energy-density materials.

A series of pyrimidine derivatives were constructed by replacing hydrogen atoms with nitro groups. To explore their thermal stability and kinetic stability, heat of formation (HOF) and dissociation energies (BDE) are calculated based on the density functional theory with the B3PW91/6-311+G(d,p)//MP2/6-311+G(d,p) method. Based on our calculations, all derivatives are confirmed stable enough to be synthesized in laboratory. To explore the detonation characters, the detonation velocity and detonation pressure are calculated by using the empirical Kamlet-Jacobs equation and good detonation parameters were confirmed for most of title molecules. Based on our calculations, four molecules (2,4,5,6-tetranitropyrimidine, 4,5,6-trinitropyrimidine, 2,4,6-trinitropyrimidine, 2,4,5-trinitropyrimidine ) are screened out as potential high-energy-density materials for further research.

Thermal stability and detonation character of nitro-substituted derivatives of imidazole.

A series of nitro-imidazole derivatives were designed by replacing hydrogen atoms on imidazole ring with nitro group one by one. In order to investigate the thermodynamic stability, heat of formation (HOF), and bond dissociation energy (BDE) are calculated at the B3PW91/6-311+G(d,p) level. In order to investigate the impact sensitivity and detonation property, the drop height (H50), free space per molecule in crystal lattice (ΔV), detonation velocity (D), and detonation pressure (P) are calculated by using the empirical Kamlet-Jacobs (K-J) equation. The results show that the thermal stabilities of title molecules are determined by whether nitro group is associated to 1-position or not and accompanied with the steric hindrance between nitro groups and the charge population on the carbon atoms of imidazole ring. The excellent impact sensitivity and detonation performance of title molecules are also evaluated. On the consideration both of stability and detonation characters, 2,4,5-trinitro-1H-imidazole (D = 8.98 km/s, P = 36.70 GPa) is screened out as the potential high-energy-density molecule for further research.

Theoretical calculations about nitro-substituted pyridine as high-energy-density compounds (HEDCs).

A series of derivatives of pyridine were designed through substituting hydrogen atoms by nitro groups systematically. By using the density functional theory at B3PW91/6-311++G(d,p)//MP2/311++G(d,p) level, heats of formation, bond orders, and bond dissociation energies were calculated to explore the thermodynamic stabilities of title molecules. Furthermore, the regularity of stability was explained based on the electronic population. Our results indicated that title molecules had enough stability to exist. To evaluate the potential usage as a high-energy-density molecule, the detonation pressure and detonation velocity were explored by using the semi-empirical Kamlet-Jacobs equation and excellent detonation character was confirmed. Overall consideration of the thermal stability and energetic character, four molecules (2,3,4,5-tetranitropyridine, 2,3,5,6-tetranitropyridine, 2,4,5,6-tetranitrop-pyridine, 2,3,4,5,6-pentanitropyridine) were confirmed to be better than RDX and filtered as potential energetic molecules.

Is 1-nitro-1-triazene a high energy density material?

An azo bridge (-N=N-) can not only desensitize explosives but also dramatically increase their heats of formation and explosive properties. Amino and nitro are two important high energy density functional groups. Here, we present calculations on 1-nitro-1-triazene (NH2-N=N-NO2). Thermal stability and detonation parameters were predicted theoretically at CCSD(T)/6-311G* level, based on the geometries optimized at MP2/6-311G* level. It was found that the p→π conjugation interaction and the intramolecular hydrogen bonding that exist in the system together increase the thermal stability of the molecule. Moreover, the detonation parameters were evaluated to be better than those of the famous HMX and RDX. Finally, the compound was demonstrated to be a high energy density material.

Looking for high energy density compounds among polynitraminepurines.

A series of purine derivatives with nitramine groups are calculated by using density functional theory (DFT). The molecular theory density, heats of formation, bond dissociation energies and detonation performance are investigated at DFT-B3LYP/6-311G** level. The isodesmic reaction method is employed to calculate the HOFs of the energies obtained from electronic structure calculations. Results show that the position of nitramine groups can influence the values of HOFs. The bond dissociation energies and the impact sensitivity are analyzed to investigate the thermal stability of the purine derivatives. The calculated bond dissociation energies of ring-NHNO2 and NH-NO2 bond show that the NH-NO2 bond should be the trigger bond in pyrolysis processes. The H50 of most compounds are larger than that of CL-20 and RDX.

Computational studies on polynitropurines as potential high energy density materials.

As part of a search for high energy density materials (HEDMs), a series of purine derivatives with nitro groups were designed computationally. The relationship between the structures and the performances of these polynitropurines was studied. Density functional theory (DFT) at the B3LYP/6-311G** level was employed to evaluate the heats of formation (HOFs) of the polynitropurines by designing an isodesmic reaction method. Results indicated that the HOFs were influenced by the number and positions of substituent groups. Detonation properties were evaluated using the Kamlet-Jacobs equations, based on the theoretical densities and heats of formation of the polynitropurines. The relative stabilities of the polynitropurines were studied via the pyrolysis mechanism and the UB3LYP/6-311G** method. Homolysis of the ring-NO2 bond is predicted to be the initial step in the thermal decomposition of these purine derivatives. Considering their detonation properties and relative stabilities, the tetranitropurine (D1) derivatives may be regarded as potential candidates for practical HEDCs. These results may provide useful information for further investigations.

Looking for high energy density compounds among polynitraminecubanes.

Based on fully optimized geometric structures at DFT-B3LYP/6-311G** level, we calculated electronic structures, heats of formation, strain energies, bond dissociation energies and detonation performance (detonation velocity and detonation pressure) for a series of polynitraminecubanes. Our results have shown that energy gaps of cubane derivatives are much higher than that of triaminotrinitrobenzene (TATB), which means that cubane derivatives may be more sensitive than TATB. Polynitraminecubanes have high and positive heats of formation, and a good linear relationship between heats of formation and nitramine group numbers was presented. As the number of nitramine groups in the molecule increases, the enthalpies of combustion values are increasingly negative, but the specific enthalpy of combustion values decreases. It is found that all cubane derivatives have high strain energies, which are affected by the number and position of nitramine group. The calculated bond dissociation energies of C-NHNO(2) and C-C bond show that the C-C bond should be the trigger bond in the pyrolysis process. It is found that detonation velocity (D), detonation pressure (P) and molecule density (ρ) have good linear relationship with substituented group numbers. Heptanitraminecubane and octanitraminecubane have good detonation performance over 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), and they can be regarded as potential candidates of high energy density compounds (HEDCs). The results have not only shown that these compounds may be used as HEDCs, but also provide some useful information for further investigation.

Theoretical investigation on detonation performances and thermodynamic stabilities of the prismane derivatives.

Based on DFT-B3LYP/6-311G** method, the molecular geometric structures of polynitramineprismanes are fully optimized. The detonation performances, energy gaps, strain energies, as well as their stability were investigated to look for high energy density compounds (HEDCs). Our results show that all polynitramineprismanes have high and positive heat of formation. To construct the relationship between stabilities and structures, energy gaps and bond dissociation energies are calculated, and these results show that the energy gaps of prismane derivatives are much higher than that of TATB (0.1630). In addition, the C-C bonds on cage are confirmed as trigger bond in explosive reaction. All polynitramineprismanes have large strain energies, and the strain energies of all compounds are slightly smaller than prismane, which indicated that the strain energies were somewhat released compared to prismane. Considering the quantitative criteria of HEDCs, hexanitramineprismane is a good candidate of high energy compounds.

The valence and Rydberg excited states of CH2: a theoretical exploration.

Using the completed active space second-order perturbation (CASPT2) method, valence and Rydberg excited states of CH(2) molecule are probed with the large atomic natural orbital (ANO-L) basis set. Five states are optimized and the geometric parameters are in good agreement with the available data in literatures, furthermore, the state of 2(1)B(1) is obtained for the first time. Valence and Rydberg excited states of CH(2) are also calculated for the vertical transitions with the ANO-L+ basis set that is constructed by adding a set of 1s1p1d Rydberg orbitals into the ANO-L basis set. Two Rydberg states of the p(~3)A(2) and r(~3) B(1) at 9.88 and 10.50 eV are obtained for the first time, and the 3a(1) → 3d(yz) nature of the state p(~3)A(2) and the 3a(1) → d(x2-y2) nature of the state r(~3)B(1) are confirmed.

Density functional theory calculations on the thermodynamic properties of polynitrosoprismanes.

A series of polynitrosoprismanes, C(6)H(6 - n )(NO)( n ) (n = 1-6), considered as high energy density compounds (HEDCs), have been designed computationally. We calculated the electronic structures, the heats of formation, the specific enthalpies of combustion, the bond dissociation energies, and the strain energies of the title compounds using density functional theory (DFT) with the 6-311G** basis set. It was found that the ΔE (LUMO-HOMO) values of the title compounds decrease as the number of nitroso groups increase, and the energy gaps of the prismane derivatives are much lower than that of TATB. Their high positive heats of formation indicate that polynitrosoprismanes can store a great deal of energy. Furthermore, the HOFs for the nitrosoprismane series were observed to decrease until three nitroso groups were connected to the prismane skeleton. For the polynitrosoprismanes, the trigger bond was confirmed to be the C-C bond in the skeleton. According to our calculations, all nitrosoprismanes appear to have large strain energies, and these calculations can provide basic information that may prove useful for the molecular design of novel high energy density materials.

Theoretical investigation on the heats of formation and detonation performance in polydinitroaminocubanes.

A series of polydinitroaminocubanes have been designed computationally. We calculated the heats of formation, the detonation velocity (D) and detonation pressure (P) of the title compounds by density function theory (DFT) with 6-311 G** basis set. The relationship between the heats of formation and the molecular structures is discussed. The result shows that all cubane derivatives have high and positive heats of formation, which increase with increasing number of dinitroamino groups. The detonation performances of the title compound were estimated by Kamlet-Jacobs equation, and the result indicated that most cubane derivatives have good detonation performance over RDX (hexahydro-1,3,5-trinitro-1,3,5-trizine) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane). In addition, we also found that the heat of detonation (Q) is another very important impact in increasing detonation performance except density. The relative stabilities of the title compound are discussed in the terms of the calculated heats of formation, and the energy gaps between the frontier orbitals. The results have not only shown that these compounds may be used as high energy density compounds (HEDCs), but also provide some useful information for further investigation.

Density functional calculations for a high energy density compound of formula C6H 6-n (NO 2) n.

A series of polynitroprismanes, C(6)H(6-n )(NO(2))(n) (n = 1-6) intended for use as high energy density compounds (HEDCs) were designed computationally. Their electronic structures, heats of formation, interactions between nitro groups, specific enthalpies of combustion, bond dissociation energies, and explosive performances (detonation velocities and detonation pressures) were calculated using density functional theory (DFT) with the 6-311 G** basis set. The results showed that all of the polynitroprismanes had high positive heats of formation that increased with the number of substitutions for the prismane derivatives, while the specific enthalpy of combustion decreased as the number of nitro groups increased. In addition, the range of enthalpy of combustion reducing is getting smaller. Interactions between ortho (vicinal) groups deviate from the group additivity rule and decrease as the number of nitro groups increases. In terms of thermodynamic stability, all of the polynitroprismanes had higher bond dissociation energies (BDEs) than RDX and HMX. Detonation velocities and detonation pressures were estimated using modified Kamlet-Jacobs equations based on the heat of detonation (Q) and the theoretical density of the molecule (ρ). It was found that ρ, D, and P are strongly linearly related to the number of nitro groups. Taking both their energetic properties and thermal stabilities into account, pentanitroprismane and hexanitroprismane are potential candidate HEDCs.

Theoretical calculation about the valence and Rydberg excited states of hydrogen cyanide.

The singlet and triplet excited states of hydrogen cyanide have been computed by using the complete active space self-consistent field and completed active space second order perturbation methods with the atomic natural orbital (ANO-L) basis set. Through calculations of vertical excitation energies, we have probed the transitions from ground state to valence excited states, and further extensions to the Rydberg states are achieved by adding 1s1p1d Rydberg orbitals into the ANO-L basis set. Four singlet and nine triplet excited states have been optimized. The computed adiabatic energies and the vertical transition energies agree well with the available experimental data and the inconsistencies with the available theoretical reports are discussed in detail.

Theoretical study on the mechanism of the NCO + HCNO reaction.

The complex doublet potential surface of the NCO + HCNO reaction has been investigated at the QCISD(T)/6-311g(d,p)//UB3LYP/6-31G(d,p) level. We have found 29 isomers on the potential surface, which are connected by 38 transition states. The single-point energy calculations are performed at the high-level QCISD(T)/6-311G(d,p) for more accurate energy values. In various possible initial association ways, the end-N attack leading to HC2N2O2 a1 and a2 is the most favorable association way through a barrierless process. Through the thermodynamic and kinetic analyses, the product NO + CO + HCN should be the major product in both the low- and high-temperature conditions for its low-energy determination transition state. Our calculation is consistent with the available data in low-temperature condition and expected to be confirmed in the high-temperature condition.

A theoretical investigation of the excited states of OCLO radical, cation, and anion using the CASSCF/CASPT2 method.

Using the complete active space self-consistent field method with a large atomic natural orbital basis set, 10, 13, and 9 electronic states of the OClO radical, OClO(+) cation, and OClO(-) anion were calculated, respectively. Taking the further correlation effects into account, the second-order perturbation (CASPT2) calculations were carried out for the energetic calibration. The photoelectron spectroscopy of the OClO radical and OClO(-) anion were extensively studied in the both case of the adiabatic and vertical ionization energies. The calculated results presented the relatively complete assignment of the photoelectron bands of the experiments for OClO and its anion. Furthermore, the Rydberg states of the OClO radical were investigated by using multiconfigurational CASPT2 (MS-CASPT2) theory under the basis set of large atomic natural orbital functions augmented with an adapted 1s1p1d Rydberg functions that have specially been built for this study. Sixteen Rydberg states were obtained and the results were consistent with the experimental results.

Theoretical studies on the low-lying electronic states of the HSO neutral radical and its cation.

Using the complete active space self-consistent field (CASSCF) method with large atomic natural orbital (ANO-L) basis set, four electronic states of the HSO neutral radical are optimized. The vertical transitions of the HSO neutral radical are investigated by using the same method under the basis set of ANO-L functions augmented with a series of adapted 1s1p1d Rydberg functions, through which eight valence states and eight Rydberg states are probed. Ionic states of the HSO neutral radical are extensively studied in both cases of the adiabatic and vertical ionization, from which the relatively complete understanding of ionization energies is given. To include further correlation effects, the second-order perturbation method (CASPT2) is implemented, and the comparison between CASSCF and CASPT2 methods is performed.