NO2 Bond Dissociation Research Articles

Size-dependent reactivity of Rh cationic clusters to reduce NO by CO in the gas phase at high temperatures.

The reactivity of the reduction of NO pre-adsorbed on Rh2-9+ clusters by CO was investigated using a combination of an alternate on-off gas injection method and thermal desorption spectrometry. The reduction of RhnNxOy+ clusters by CO was evaluated by varying the CO concentration at T = 903 K. Among the RhnNxOx+ clusters, the Rh3N2O2+ cluster exhibited the highest reduction activity, whereas the other clusters, Rh2,4-9NxOx+, showed lower reactivity. Density functional theory (DFT) calculations for Rh3+ and Rh6+ revealed that the rate-determining step for NO reduction in the presence of CO was NO bond dissociation through the kinetics analysis using the RRKM theory. The reduction of Rh3N2O2+ is kinetically preferable to that of Rh6N2O2+. The DFT results were in qualitative agreement with the experimental results.

Visible-light NO photolysis of ruthenium nitrosyl complexes with N2O2 ligands bearing π-extended rings and their photorelease dynamics.

NO photorelease and its dynamics for two {RuNO}6 complexes, Ru(salophen)(NO)Cl (1) and Ru(naphophen)(NO)Cl (2), with salen-type ligands bearing π-extended systems (salophenH2 = N,N'-(1,2-phenylene)-bis(salicylideneimine) and naphophenH2 = N,N'-1,2-phenylene-bis(2-hydroxy-1-naphthylmethyleneimine)) were investigated. NO photolysis was performed under white room light and monitored by UV/Vis, EPR, and NMR spectroscopies. NO photolysis was also performed under 459 and 489 nm irradiation for 1 and 2, respectively. The photochemical quantum yields of the NO photolysis (ΦNO) of both 1 and 2 were determined to be 9% at the irradiation wavelengths. The structural and spectroscopic characteristics of the complexes before and after the photolysis confirmed the conversion of diamagnetic Ru(II)(L)(Cl)-NO+ to paramagnetic S = ½ Ru(III)(L)(Cl)-solvent by photons (L = salophen2- and naphophen2-). The photoreleased NO radicals were detected by spin-trapping EPR. DFT and TDDFT calculations found that the photoactive bands are configured as mostly the ligand-to-ligand charge transfer (LLCT) of π(L) → π*(Ru-NO), suggesting that the NO photorelease was initiated by the LLCT. Dynamics of NO photorelease from the complexes in DMSO under 320 nm excitation were investigated by femtosecond (fs) time-resolved mid-IR spectroscopy. The primary photorelease of NO occurred for less than 0.32 ps after the excitation. The rate constants (k-1) of the geminate rebinding of NO to the photolyzed 1 and 2 were determined to be (15 ps)-1 and (13 ps)-1, respectively. The photochemical quantum yields of NO photolysis (ΦNO, λ = 320 nm) were estimated to be no higher than 14% for 1 and 11% for 2, based on the analysis of the fs time-resolved IR data. The results of fs time-resolved IR spectroscopy and theoretical calculations provided some insight into the overall kinetic reaction pathway, localized electron pathway or resonance pathway, of the NO photolysis of 1 and 2. Overall, our study found that the investigated {RuNO}6 complexes, 1 and 2, with planar N2O2 ligands bearing π-extended rings effectively released NO under visible light.

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.

Initial Mechanisms for the Unimolecular Thermal Decomposition of 2,6-Diamino-3,5-dinitropyrazine-1-oxide.

The initial channels of thermal decomposition mechanism of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) molecule were investigated. The results of quantum chemical calculations revealed four candidates involved in the reaction pathway, including the C–NO2 bond homolysis, nitro–nitrite rearrangement followed by NO elimination, and H transfer from amino to acyl O and to nitro O with the subsequent OH or HONO elimination, respectively. In view of the further kinetic analysis and ab initio molecular dynamics simulations, the C–NO2 bond homolysis was suggested to be the dominant step that triggered the decomposition of LLM-105 at temperatures above 580 K. Below this temperature, two types of H transfer were considered as the primary reactions, which have advantages including lower barrier and high rate compared to the C–NO2 bond dissociation. It could be affirmed that these two types of H transfer are reversible processes, which could buffer against external thermal stimulation. Therefore, the excellent thermal stability of LLM-105, that is nearly identical to that of 1,3,5-triamino-2,4,6-trinitrobenzene, can be attributed to the reversibility of H transfers at relatively low temperatures. However, subsequent OH or HONO elimination reactions occur with difficulty because of their slow rates and extra energy barriers. Although nitro–nitrite rearrangement is theoretically feasible, its rate constant is too small to be observed. This study facilitates the understanding of the essence of thermal stability and detailed decomposition mechanism of LLM-105.

Thermal Decomposition Mechanism of 2,2′,4,4′,6,6′-Hexanitrostilbene by ReaxFF Reactive Molecular Dynamics Simulations

2,2′,4,4′,6,6′-Hexanitrostilbene (HNS) is an explosive with increased heat resistance, and its mechanism of thermal decomposition is of interest. In this paper, the decomposition processes of HNS at various temperatures (2500, 2750, 3000, 3250, and 3500 K) are calculated by large-scale reactive molecular dynamics simulations. The initial reactions and the evolution of clusters (whose molecular weight is larger than HNS) are analyzed. The reaction kinetics parameters are fitted. The results show that the main initial decomposition mechanisms of HNS are C–NO2 bond dissociation and nitro-nitrite (NO2–ONO) isomerization. During decomposition, O atoms are less likely to be released from the cluster than H and N atoms. Low temperatures tend to produce larger clusters, and clusters at higher temperatures tend to decompose. The thermal decomposition of HNS is a combination of single-molecule and bimolecular decomposition mechanisms. The dimerization reaction is clearly weakened, and the C–N bond cleavage is still...

Shock response of condensed-phase RDX: molecular dynamics simulations in conjunction with the MSST method.

We have performed molecular dynamics simulations in conjunction with the multiscale shock technique (MSST) to study the initial chemical processes of condensed-phase RDX under various shock velocities (8 km s−1, 10 km s−1 and 11 km s−1). A self-consistent charge density functional tight-binding (SCC-DFTB) method was used. We find that the N–NO2 bond dissociation is the primary pathway for RDX with the NO2 groups facing (group 1) the shock, whereas the C–N bond scission is the dominant primary channel for RDX with the NO2 groups facing away from (group 2) the shock. In addition, our results present that the NO2 groups facing away from the shock are rather inert to shock loading. Moreover, the reaction pathways of a single RDX molecule under the 11 km s−1 shock velocity have been mapped out in detail, NO2, NO, N2O, CO and N2 were the main products.

Novel Nitrogen‐Rich Tetrazine‐Based High Energy Density Molecules: Molecular Design and Computational Studies

AbstractThe molecular structure, thermal stability, detonation properties and impact sensitivity of nitrogen‐rich tetrazine‐based designed high energy density molecules are examined. The effective stability of the designed molecules in terms of electronic structure, thermal excitation, photo‐excitation and in presence of water are predicted. The topography of the excited and ground state (S1 and S0) of those molecules along the C−NO2 bond dissociation coordinate are studied. The existence of the double minima at the S1 state and the S1‐S0 intersection produces a probabilistic path for molecules B1, B2 and A1, to revert back to their respective S0 state from the S1 state via both radiative and non‐radiative deactivation mechanism. The energy content (in terms of heats of formation), detonation velocities and detonation pressure of tetrazine‐based molecules are measured. Interestingly, the thermal stability of these designed molecules is higher than the two well‐known high energy density molecules: RDX and HMX. The detonation velocities and the detonation pressure of these molecules are higher than RDX, however, are lower than HMX. In addition, the safety, reliability and stability of these high energy density molecules have been measured by formulating semi‐empirical equations of impact sensitivity based on linear and multiple linear regression method and the present study is ended with the discussion of most probable synthetic routes to the designed molecules.

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.

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.

Computational screening of several silicon-based high-energy hexanitrohexaazaisowurtzitane-like derivatives

Silicon-based hexanitrohexaazaisowurtzitane (CL-20) derivatives, including nitro (NO2) and difluoramino (NF2) group containing derivatives, may become important high-energy compounds. Density Functional Theory Becke exchange plus Perdew correlation (BP) with triple numerical set plus polarization functions (TNP) and homodesmotic reactions were employed to calculate cage strain energies, gaseous phase formation enthalpies of several silicon-based CL-20 derivatives. Comparative studies were carried out between silicon-based CL-20 nitro and difluoramine derivatives. The structural stability of these silicon-based CL-20 derivatives were evaluated in terms of NNO2 or NNF2 bond dissociation energies and Mulliken charges of NO2 or NF2 groups by means of density functional theory revised versions of the Perdew–Burke–Ernzerhof (RPBE) with TNP functions, and the exchange component of Perdew and Wang's 1991 functional (PW91) with TNP functions, two theoretical methods were chosen according to experimental data. The theoretical studies show that their performances are better than CL-20 in terms of detonation velocities, detonation pressures and explosion temperatures. Structural stability of these silicon-based CL-20 derivatives is higher than CL-20 according to NNO2 or NNF2 bond dissociation energies and cage strain energies. This work will lay some foundations for the future explorations of novel high-energy silicon-based compounds.

PCM Study of Bond Dissociation Energies of the S–NO Bond: A DFT Study

Quantum chemical calculations are used to estimate the equilibrium S–NO bond dissociation energies (BDEs) for seven S-nitro-N-acetyl-d,l-penicillamine dipeptides (SNAP-two peptides) in acetonitrile solution. These compounds were studied by employing the hybrid density functional theory (B3LYP, B3P86 and B3PW91) methods together with the 6-31G** basis set. The obtained results are compared with available experimental results. It is demonstrated that B3PW91 method is the best method to compute the bond dissociation energies of SNAP-two peptides. The substituent and solvent effects of the S–NO BDEs are further analyzed. The results show that S–NO BDE increases with the increment of isoelectric points of substituted groups. In addition, the S–NO BDE decreases due to the inclusion of solvent effects. Furthermore, SNAP-two peptides and the other NO-donors are compared.

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).

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO2

Allyl radical reactions with NO and NO(2) were studied in direct, time-resolved experiments in a temperature controlled tubular flow reactor connected to a laser photolysis/photoionization mass spectrometer (LP-PIMS). In the C(3)H(5) + NO reaction 1 , a dependence on the bath gas density was observed in the determined rate coefficients and pressure falloff parametrizations were performed. The obtained rate coefficients vary between 0.30-14.2 × 10(-12) cm(3) s(-1) (T = 188-363 K, p = 0.39-23.78 Torr He) and possess a negative temperature dependence. The rate coefficients of the C(3)H(5) + NO(2) reaction 2 did not show a dependence on the bath gas density in the range used (p = 0.47-3.38 Torr, T = 201-363 K), and they can be expressed as a function of temperature with k(C(3)H(5) + NO(2)) = (3.97 ± 0.84) × 10(-11) × (T/300 K) (-1.55±0.05) cm(3) s(-1). In the C(3)H(5) + NO reaction, above 410 K the observed C(3)H(5) radical signal did not decay to the signal background, indicating equilibrium between C(3)H(5) + NO and C(3)H(5)NO. This allowed the C(3)H(5) + NO ⇄ C(3)H(5)NO equilibrium to be studied and the equilibrium constants of the reaction between 414 and 500 K to be determined. With the standard second- and third-law analysis, the enthalpy and entropy of the C(3)H(5) + NO ⇄ C(3)H(5)NO reaction were obtained. Combined with the calculated standard entropy of reaction (ΔS°(298) = 137.2 J mol(-1)K(-1)), the third-law analysis resulted in ΔH°(298) = 102.4 ± 3.2 kJ mol(-1) for the C(3)H(5)-NO bond dissociation enthalpy.

Combined theoretical and experimental study on the molecular structure, FT-IR, and NMR spectra of cyadox and 1,4-bisdesoxycyadox

1,4-Bisdesoxycyadox, a deoxidized metabolite of cyadox, was synthesised and characterized. Structural and conformational analyses were performed using theoretical calculations employing density functional theory (DFT). The molecular geometry was optimized using B3LYP method with 6-311+G(d,p) basis set and then it was compared with X-ray diffraction data of similar molecular compounds. From the optimized geometry of the molecule, vibrational frequencies of the title compounds were calculated via B3LYP/6-311+G(d,p) approach. The 1H and 13C NMR chemical shift were calculated by gauge-including atomic orbital method with B3LYP/6-311++G(2df,2pd) approach. Comparison of the experimental and calculated 1H and 13C chemical shifts resulted in the reliable assignment of cyadox and 1,4-bisdesoxycyadox. The first, second, total, and mean NO bond dissociation enthalpies were also obtained theoretically.

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.

Convenient synthesis of quinocetone metabolites: Characterization, theoretical investigation, and cytotoxicity study

Quinocetone (3-methyl-2-quinoxalinbenzenevinylketo-1,4-dioxide; QCT) is a new promising antimicrobial growth promoter for quinoxalines. The identification of the major metabolites of QCT has resulted in a number of studies regarding its metabolic pathway. However, little is known about the systematic synthesis, characterization, and simultaneous determination of its metabolites. To obtain system data for the four main metabolites of QCT, a convenient synthesis of these compounds was performed. All synthesized compounds were characterized by infrared spectroscopy, nuclear magnetic resonance, and high-resolution mass spectroscopy. The theoretical NO bond dissociation enthalpies (BDEs) and octanol–water partition coefficient (Kow) were estimated. A cytotoxicity assay for these compounds in hepatocytes isolated from rats was proposed, and the cytotoxicity results were evaluated based on the calculated NO BDEs.

DFT-PCM Study of the Bond Dissociation Energies of N-nitrosoindole Compounds in Acetonitrile

Quantum chemical calculations are used to estimate the equilibrium N–NO bond dissociation energies (BDEs) in acetonitrile (MeCN) for seven N-nitrosoindole compounds. These compounds are studied by employing the hybrid density functional theory (B3LYP, B3P86 and B3PW91) methods together with 6-31G∗∗ basis sets. The obtained results are compared with the available experimental results. It is demonstrated that the B3PW91 method is the best of these methods to compute the bond dissociation energies of N-nitrosoindole compounds. The solvent effects on the BDEs of the N–NO bond are analyzed and it is shown that the N–NO BDEs in a vacuum, computed by the B3LYP method, are the closest to the computed values in MeCN and the average solvent effect is 4.0 kJ⋅mol−1. The substituent effects on the N–NO BDEs were further analyzed and it is found that the N–NO BDE increases with increments of the Hammett constants of substituent groups on the benzene ring for N-nitrosoindole compounds, except the compound with 5-NO2−C8H5N–NO. Finally, N-nitrosoindole compounds and the other NO-donors (N-nitroso compounds) are compared.