NO2 Bond Dissociation Energies Research Articles

Quantum Mechanical Investigation on Decomposition Pathways of BuNENA

AbstractThe unimolecular decomposition pathways of n‐butyl nitroxyethylnitramine (BuNENA) were computationally investigated. The O−NO2 bond dissociation energies (BDEs) are found to be smaller than the N−NO2 BDEs. The consecutive NO2 elimination via TSA1 is more favorable kinetically than that via TSA2 although both of them form the same intermediate of n‐butyl‐aminoacetaldehyde (BuAAA). Isomerization of n‐butyl‐nitramineethyloxidanyl radical (BuNEȮ) formed by homolytic cleavage of O−NO2 bond was found to eliminate NO2 with a negative bond dissociation energy. Among the NO2 elimination pathways, the formation of C4H9NCH2 (PB2b), CH2O, and NO2 from BuNEȮ via the saddle point TSB2a was found to be the most kinetically favorable with a low activation energy barrier. In contrast, the consecutive HONO elimination is the most thermodynamically favorable with a high exothermicity (−▵H0). The first‐principle kinetic Monte Carlo (kMC) simulations show that the NO2 elimination of BuNEȮ via TSB2a plays an important role in driving the decomposition of BuNENA.

The effect of molecular structure on the O – NO2 bond dissociation energy and the activation energy of the radical decay of cellotriose nitrates

The molecular structure was determined using the method B3LYP/6-31+G(2df, p), and the dissociation energies of the O – NO2 bond in dimethylcellobiose and cellotriose nitrates were calculated. It has been established that the O – NO2 bonds attached to the secondary carbon atom at C2 are the least strong in cellotriose nitrates. With an increase in the degree of substitution, a slight decrease in the dissociation energy of radical decay is observed. The results can be used to discuss the mechanism of thermal decomposition of cellulose nitrates.

Kinetic and Mechanistic Study of the Thermal Decomposition of Ethyl Nitrate

Thermal decomposition of ethyl nitrate (ENT; CH3CH2ONO2) has been studied in a low-pressure flow reactor combined with a quadrupole mass spectrometer. The rate constant of the nitrate decomposition was measured as a function of pressure (1–12.5 Torr of helium) and temperature in the range 464–673 K using two different approaches: from kinetics of ENT loss and those of the formation of the reaction product (CH3 radical). The fit of the observed falloff curves with two-parameter expression provided the following low- and high-pressure limits for the rate constant of ENT decomposition: k0 = 1.0 × 10−4 exp(−16,400/T) cm3 molecule−1 s−1 and k∞ = 1.08 × 1016 exp(−19,860/T) s−1, respectively, which allow to reproduce (via above expression and with 20% uncertainty) all the experimental data obtained for k1 in the temperature and pressure range of the study. It was observed that the initial step of the thermal decomposition of ethyl nitrate is O–NO2 bond cleavage leading to formation of NO2 and CH3CH2O radical, which rapidly decomposes to form CH3 and formaldehyde as final products. The yields of NO2, CH3, and formaldehyde upon decomposition of ethyl nitrate were measured to be near unity. In addition, the kinetic data were used to determine the O–NO2 bond dissociation energy in ENT: 38.3 ± 2.0 kcal mol−1.

A computational study on new oxidizers as replacements for ammonium perchlorate: tetranitroacetimidic acid and tetranitroacetamide

High energetic materials tetranitroacetimidic acid (TNAA) and tetranitroacetamide (NTNAA) with positive oxygen balance (OB = 30%) are highly potential replacements for ammonium perchlorate (AP). Tautomerization from TNAA to NTNAA is feasible, reflected by the activation energy of 160.2∼170.0 kJ/mol. No transition state appears on the C–NO2 bond breaking, which triggers pyrolysis of two compounds. The C–NO2 bond dissociation energies are 116.1∼167.2 kJ/mol and 120.4∼174.6 kJ/mol for TNAA and NTNAA, respectively. The chemical stabilities of TNAA and NTNAA are higher than that of the insensitive explosive 1,1-diamino-2,2-dinitroethylene. TNAA and NTNAA possess lower impact sensitivities (h50 ≥ 77.51 cm) than AP does. Detonation properties of the composite explosives containing TNAA or NTNAA are comparable with that of the composite explosives containing AP. The acceptable stabilities, highly positive OB, environmentally friendly decomposition products, and the comparable ability to improve detonation performance of composite explosives show that TNAA and NTNAA are potential replacements for AP as an oxidizer used in composite explosives.

Theoretically predicted Fox-7 based new high energy density molecules

Computational investigation of CHNO based high energy density molecules (HEDM) are designed with FOX-7 (1, 1-dinitro 2, 2-diamino ethylene) skeleton. We report structures, stability and detonation properties of these new molecules. A systematic analysis is presented for the crystal density, activation energy for nitro to nitrite isomerisation and the C–NO2 bond dissociation energy of these molecules. The Atoms in molecules (AIM) calculations have been performed to interpret the intra-molecular weak H-bonding interactions and the stability of C–NO2 bonds. The structure optimization, frequency and bond dissociation energy calculations have been performed at B3LYP level of theory by using G03 quantum chemistry package. Some of the designed molecules are found to be more promising HEDM than FOX-7 molecule, and are proposed to be candidate for synthetic purpose.

Theoretical Insight into the Influences of Molecular Ratios on Stabilities and Mechanical Properties, Solvent Effect of HMX/FOX-7 Cocrystal Explosive

A molecular dynamics method was employed to study the binding energies of the selected crystal planes of the 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane/1,1-diamino-2,2-dinitroethylene (HMX/FOX-7) cocrystal in different molecular molar ratios. Mechanical properties, densities, and detonation velocities of the cocrystals in different ratios were estimated. The intermolecular interactions and bond dissociation energies (BDEs) of the N–NO2 bond in the HMX:FOX-7 (1:1) complex were calculated using the B3LYP and MP2(full) methods at the 6–311++G (d,p) and 6–311++G(2df,2p) basis sets. Solvent effects on stability are discussed. The results indicate that HMX/FOX-7 cocrystals prefer cocrystalizing in a 1:1 molar ratio, which has good mechanical properties. The N–NO2 bond becomes strong upon the formation of a complex and the sensitivity of HMX might decrease in cocrystals. The sensitivity change of HMX/FOX-7 originates from not only the formation of intermolecular interaction but also the increment in the N–NO2 BDE. HMX/FOX-7 cocrystals exhibit good detonation performance and meet the requirements of high-density energetic materials. Solvents with low dielectric constants may be chosen to obtain stable HMX/FOX-7 cocrystals.

Interaction of an α‐Particle with TATB

AbstractInteraction of an alpha particle with triaminotrinitrobenzene (TATB) which is an insensitive explosive has been investigated by density functional calculations. It has been found that α‐particles interact with TATB disturbing its planar geometry. As a result, the C–NO2 bond dissociation energies are substantially decreased, whereas detonation velocity and pressure values increased as compared to TATB. The quantum chemical properties of the structures are presented.

N[sbnd]NO2 bond dissociation energies in acetonitrile: An assessment of contemporary computational methods

The assessment of the NNO2 bond dissociation energies (BDEs) was performed by various calculating methods (B3LYP, B3PW91, B3P86, B1LYP, BMK, MPWB1K, PBE0, CBS-4M and M06-2X) at 6-311+G(2d,p) basis set. Compared with the experimental BDEs, the results show that BMK and B3P86 methods reproduce the experimental values well. The mean absolute deviations from the experimental values obtained by BMK and B3P86 methods were 0.5 and 1.5kcal/mol, respectively. B3LYP, B3PW91, B1LYP, MPWB1K and PBE0 methods underestimated the homolytic NNO2 BDEs. B3LYP, B3PW91, B1LYP, M06-2X, CBS-4M methods failed to provide an accurate description of NNO2 BDEs for N-Nitrosulfonamide compounds and showed larger mean absolute deviations and maximum deviations. Further, substituent effect based on BMK/6-311+G(2d,p) method was analysis. Natural bond orbital analysis shows that there exist good linear correlations between E(2) of lpN1→BD*(O1N2) and Hammett constants and a better correlation between the BDEs and the second order stabilization energy E(2) of lpN1→BD*(O1N2).

Density functional theory for N–NO2 bond dissociation energies of N-nitroacylamide compounds in acetonitrile — Theoretical method assessment and prediction

The performance of various density functional theories (B3LYP, B3PW91, B3P86, B1LYP, BMK, MPWB1K, PBE0, and MPWB95) was examined for calculating N–NO2 bond dissociation energies (BDEs) of 10 N-nitroacylamide compounds. The CBS-4M method was also used. By comparing the calculated results with the experimental values, it was observed that B1LYP/6–31G** and B3LYP/6–31+G** provided accurate BDEs. Especially, B3LYP/6–31+G** was recommended because of its smaller maximum absolute deviation. Further, substituent effects based on the B3LYP/6–31+G** method were analyzed. The result shows that an electron-donating group increases the BDE of the parent C6H5–CON(CH3)NO2, while an electron-withdrawing group decreases the BDE of the parent C6H5–CON(CH3)NO2. Subsequently, the BDEs of the other N-nitroacylamindes were estimated.

Polarized continuum model study of bond dissociation energies of the O–NO2 bond — A density functional theory study and natural bond order analysis

Density functional methods (B3LYP, B3PW91, B3P86, and MPWB95) with 6–31G** basis sets and complete basis methods are employed to investigate the bond dissociation energies (BDEs) of the O–NO2 bond for seven O-nitroalcohol compounds in acetonitrile solution. B3LYP/6–31+G**, (RO)B3LYP/6–311++G(2df,2p), and B3LYP/6–311G(d,p) methods are also used. By comparing the calculated results with the experimental values, B3LYP/6–31+G** is the most accurate method to compute the reliable BDEs for the studied compounds. The substituent effects on the O–NO2 BDEs are analyzed. It is found that electron-withdrawing groups increase the BDE of the parent compound, whereas electron-donating groups decrease the BDE of the parent compound. Further, the natural bond orbital analysis shows that there exist good linear correlations between E(2) and Hammett constants, the BDE, and the difference of the second-order stabilization energies E(2) of lpO3 → BD*(O1–N1) and lpO3 → BD*(O2–N1).

Investigation of correlation between impact sensitivities and bond dissociation energies in some triazole energetic compounds

In this article, density functional theory has been utilized to study on the correlation between impact sensitivities h 50% and the bond dissociation energies (BDEs) of nine triazole energetic explosives. By employing B3LYP and B3P86 method with the 6-311G** basis set, all the molecules have been fully optimized. The BDEs for removal of the NO2 group in these compounds have also been calculated at the same level. Computed results show that BDEs calculated by B3LYP method are all less than those by B3P86 method. The relationship between the impact sensitivities and the weakest C–NO2 bond dissociation energy (BDE) values have been investigated. The results indicate a good linear correlation between the impact sensitivity h 50% and the ratio (BDE/E) of the weakest BDE to the total energy E.

Links between surface electrostatic potentials of energetic molecules, impact sensitivities and C–NO2/N–NO2 bond dissociation energies

Earlier work has shown a link—not necessarily a causal relationship—between the impact sensitivities of energetic compounds and the electrostatic potentials on their molecular surfaces. The latter are anomalous in that the positive regions are strikingly dominant, contrary to what is typical of organic molecules. In this work, we show that the presence of several electron-withdrawing NO2 groups and/or aza nitrogens (common features of energetic systems), which is the reason for the anomalously positive surface potentials, also weakens the C–NO2 and/or N–NO2 bonds. Thus, insofar as these are trigger linkages, the rupture of which is a key step in detonation initiation, an approximate correlation between the features of the surface potentials and sensitivity may be expected. A group of eight nitramines is used to demonstrate this. Work is in progress to elucidate the basis for the surface potential–sensitivity link when a non-trigger-linkage mechanism is operative.

Theoretical calculation of bond dissociation energies and heats of formation for nitromethane and polynitromethanes with density functional theory

AbstractThe CNO2 bond dissociation energies (BDEs) and the heats of formation (HOFs) of nitromethane and polynitromethanes (dinitromethane, trinitromethane, and tetranitromethane) system in gas phase at 298.15 K were calculated theoretically. Density functional theory (DFT) B3LYP, B3P86, B3PW91, and PBE0 methods in combination with different basis sets were employed. It was found that the CNO2 bond BDEs can be improved from B3LYP to B3PW91 to B3P86 or PBE0 functional. Levels of theory employing B3P86 and PBE0 functionals were found to be sufficiently reliable without the presence of diffusion functions. As the number of NO2 groups on the same C atom increases, the PBE0 functional performs better than the B3P86 functional. Regarding the calculated HOFs, all four functionals can yield satisfactory results with deviations of <2 kcal mol−1 from experimental ones for CH2(NO2)2 and CH(NO2)3, when the diffusion functions are not augmented. For the C(NO2)4 molecule, the large basis sets augmented with polarization functions and diffusion functions are required to yield a good result. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

The C−NO2 bond dissociation energies of some nitroaromatic compounds: DFT study

The C−NO2 bond dissociation energies in nitrobenzene; 3-amino-nitrobenze; 4-amino-nitrobenze; 1,3-dinitrobenzene; 1,4-dinitrobenzene; 2-methyl-nitrobenzene; 4-methyl-nitrobenzene; and 1,3,5-trinitrobenzene nitroaromatic molecules, are computed using B3LYP, B3PW91, B3P86 three-parameter hybrid Density Functional Theory (DFT) methods in conjunction with 6-31G** basis set. By comparing the computed energies and experimental ones, it is found that B3P86/6-31G** is not capable of predicting the satisfactory bond dissociation energy (BDE). The BDEs computed with both B3LYP/6-31G** and B3PW91/6-31G** for the nitroaromatic molecules are closer to the experimental ones than those obtained with B3P86/6-31G**. But, when compared with the experimental one, the BDE from the B3LYP/6-31G** has the maximum deviation, which is completely outside our desired target accuracy for chemical predictions (less than 2.00 kcal mol−1). Therefore, we suggest B3PW91/6-31G** method as a reliable method of computing the BDE for removal of the nitrogen dioxide group in the nitroaromatic compounds. In addition, the C−NO2 BDEs for 2,4,6-trinitrotoluene (TNT), triaminotrinitrobenzene (TATB), diaminotrinitrobenzene (DATB), and picramide are studied with B3PW91/6-31G** method.

The evaluation of bond dissociation energies for NO 2 scission in nitro compounds using density functional and complete basis set methods

By using the density functional theory (B3LYP) and four highly accurate complete basis set (CBS-Q, CBS-QB3, CBS-Lq and CBS-4M) ab initio methods, the X(C, N, O)–NO2 bond dissociation energies (BDEs) for CH3NO2, C2H3NO2, C2H5NO2, HONO2, CH3ONO2, C2H5ONO2, NH2NO2 (CH3)2NNO2 are computed. By comparing the computed BDEs and experimental results, it is found that the B3LYP method is unable to predict satisfactorily the results of bond dissociation energy (BDE); however, all four CBS models are generally able to give reliable predication of the X(C, N, O)–NO2 BDEs for these nitro compounds. Moreover, the CBS-4M calculation is the least computationally demanding among the four CBS methods considered. Therefore, we recommend CBS-4M method as a reliable method of computing the BDEs for this nitro compound system.

Calculations of the Bond Dissociation Energies for NO2 Scission in Some Nitro Compounds

The X(C,N,O)—NO2 bond dissociation energy (BDE) for CH3NO2, C2H3NO2, C2H5NO2, HONO2, CH3ONO2, C2H5ONO2, NH2NO2, (CH3)2NNO2 are computed using the DFT (B3LYP, B3PW91), the single and double-coupled cluster excited (CCSD), and the complete basis set (CBS-Q) methods, with the 6-311G** and cc-pVDZ basis sets. By comparing the computed energies and experimental results, we find that the DFT method can not give good results of BDE, but, the BDEs generated by the CCSD/cc-pVDZ, CBS-Q are in good agreement with experimental values.

00/01181 Factors governing reactivity in low temperature coal gasification. Part 1. An attempt to correlate results from a suite of coals with experiments on maceral concentrates

The assessment of the NNO2 bond dissociation energies (BDEs) was performed by various calculating methods (B3LYP, B3PW91, B3P86, B1LYP, BMK, MPWB1K, PBE0, CBS-4M and M06-2X) at 6-311+G(2d,p) basis set. Compared with the experimental BDEs, the results show that BMK and B3P86 methods reproduce the experimental values well. The mean absolute deviations from the experimental values obtained by BMK and B3P86 methods were 0.5 and 1.5 kcal/mol, respectively. B3LYP, B3PW91, B1LYP, MPWB1K and PBE0 methods underestimated the homolytic NNO2 BDEs. B3LYP, B3PW91, B1LYP, M06-2X, CBS-4M methods failed to provide an accurate description of NNO2 BDEs for N-Nitrosulfonamide compounds and showed larger mean absolute deviations and maximum deviations. Further, substituent effect based on BMK/6-311+G(2d,p) method was analysis. Natural bond orbital analysis shows that there exist good linear correlations between E(2) of lpN1 → BD*(O1N2) and Hammett constants and a better correlation between the BDEs and the second order stabilization energy E(2) of lpN1 → BD*(O1N2).

Tautomerism, Ionization, and Bond Dissociations of 5-Nitro-2,4-dihydro-3H-1,2,4-triazolone

Tautomerization, ionization, and bond dissociations of the insensitive high-energy explosive 5-nitro-2,4-dihydro-3H-1,2,4-triazolone (NTO) were studied by molecular orbital SCF and MP2 theories and with the Becke3LYP hybrid density functional using the 6-31+G* and 6-311+G** basis sets. Energies computed with these methods were compared against accurate G2 energies for the tautomerization, ionization, and bond dissociations of nitromethane. The Becke3LYP and MP2/6-31+G* structures of NTO anion 9 compare well with the reported X-ray structure of the NTO diaminoguanidinium salt. The IR frequencies calculated with Becke3LYP compare well with those observed for crystalline NTO. Two enol tautomers (2 and 4) with 1H-1,2,4-triazole skeletons are only 4 kcal/mol at MP2/6-311+G** (and 9 kcal/mol at Becke3LYP/6-311+G**) less stable than NTO, while the two aci-nitro tautomers (5 and 6) are ca. 30 kcal/mol less stable than NTO. Comparisons of bond lengths, calculated proton chemical shifts, and magnetic susceptibility anisotropies show the enol tautomers are more aromatic than NTO, which accounts for their enhanced stabilities. NTO anion 9 is also more aromatic than NTO, which partly explains its small proton affinity of 321 kcal/mol calculated at Becke3LYP/6-311+G**+ZPE. The estimated N−H and C−NO2 bond dissociation energies for NTO are respectively 93 and 70 kcal/mol, and that for the N−OH bond of the aci-nitro tautomer 5 is 38 kcal/mol. Some possible processes in the initial stages of NTO decomposition are bimolecular hydrogen atom transfers (in the condensed phase), C−NO2 bond homolysis (at high temperatures or under conditions of shock or impact), and homolysis of the N−OH bond in the aci-nitro tautomers.

Ab‐Initio MRD‐CI calculations for breaking a chemical bond in a molecule in a crystal or other solid environment. II.H3C—NO2 decomposition of nitromethane in a nitromethane crystal with voids

AbstractRecently we extended our strategy for MRD‐CI (multireference double excitation‐configuration interaction) calculations based on localized/local orbitals and an “effective” CI Hamiltonian for molecular decompositions of large molecules to breaking a chemical bond in a molecule in a crystal or other solid environment. Our technique involves solving a quantum chemical ab‐initio SCF explicitly for a system of a reference molecule surrounded by a number of other molecules in the multipole environment of more distant neighbors. The resulting canonical molecular orbitals are then localized and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD‐CI with the remainder of the occupied localized orbitals being folded into an “effective” CI Hamiltonian. The MRD‐CI calculations are carried out for breaking a bond in the reference molecule. This method is completely general. The space treated explicitly quantum chemically and the surrounding space can have voids, defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc. We previously applied this procedure successfully to the H3CNO2 bond dissociation of nitromethane in a nitromethane crystal with extensive testing of the number of molecules that have to be included explicitly in the SCF and how many molecules have to be represented by more distant multipoles. The results indicated that it took more energy to dissociate the H3CNO2 bond when the nitromethane molecule was in the crystal than it did to dissociate that bond in the free nitromethane molecule. In this present study we have investigated the effect of voids (both in the nitromethane molecules treated explicitly in the SCF and those in the environment represented by multipoles) on the calculated H3CNO2 bond dissociation energies.