NO Bond Research Articles

DFT and ab Initio Study of the Unimolecular Decomposition of the Lowest Singlet and Triplet States of Nitromethane

The fully optimized potential energy curves for the unimolecular decomposition of the lowest singlet and triplet states of nitromethane through the C−NO2 bond dissociation pathway are calculated using various DFT and high-level ab initio electronic structure methods. We perform gradient corrected density functional theory (DFT) and multiconfiguration self-consistent field (MCSCF) to conclusively demonstrate that the triplet state of nitromethane is bound. The adiabatic curve of this state exhibits a 33 kcal/mol energy barrier as determined at the MCSCF level. DFT methods locate this barrier at a shorter C−N bond distance with 12−16 kcal/mol lower energy than does MCSCF. In addition to MCSCF and DFT, quadratic configuration interactions with single and double substitutions (QCISD) calculations are also performed for the singlet curve. The potential energy profiles of this state predicted by DFT methods based on Becke's 1988 exchange functional differ by as much as 17 kcal/mol from the predictions of MCSCF ...

First Accurate Molecular and Crystal Structure of the Meisenheimer Complex of 2,4,6-Trinitrobenzene

The first accurate and reliable molecular and crystal structure of the Meisenheimer complex of 2,4,6-trinitrobenzene (potassium (1,4-dioxolane)-2-spiro-1′-2′,4′,6′-trinitrocyclohexadienide) has been obtained by X-ray diffraction. The C–NO2 bond length for the substituent in the para position of the six-membered ring is shorter than for the other ones, and the bond lengths in the unsaturated parts of the anion are not equal. These facts indicate an essential contribution of the 1,4-diene geometry of the ring as well as of the aci resonance forms of the nitro groups to the structure of the anion.

Theoretical study on pyrolysis and sensitivity of energetic compounds. Part 4. Nitro derivatives of phenols

The UHF–SCF–AM1 MO method was applied to the study of two kinds of pyrolysis reactions of six nitro derivatives of phenols (homolysis reaction by rupture of the C—NO2 bond into radicals and isomerization reaction involving phenolic hydrogen transferring to oxygen on the NO2 group). The molecular geometries of reactants, transition states and products were fully optimized. The potential energy curves and activation energies were first obtained. The results show that this category of compounds is more easily initiated via isomerization reactions than by homolysis reactions. The parallel relationship among the Wiberg bond order of the pyrolysis-initiation H—O bond in the molecule of a reactant, the activation energy of the isomerization reaction breaking the H—O bond and impact sensitivity of the reactant gives ‘the principle of the smallest bond order’ (PSBO) powerful support. The sensitizing effect of a phenol group was elucidated based on calculation results. The different influences of OH and NO2 groups on the heat of formation of a molecule are discussed. © 1998 John Wiley & Sons, Ltd.

Mechanism of the primary stages of decomposition of aliphatic nitro- and fluoronitronitramines

The primary stage of the decomposition of compounds RN(NO2)CH2C(NO2)2X is the homolytic cleavage of the C−NO2 bond, at X=NO2 and N−NO2 bond at X=F. The inductive effect of substituents decreases the dissociation energies of the C−N and N−N bonds by 1–2 kcal mol−1. Kinetic effects caused by the spatial interaction of groups and by stepwise decomposition of polyfunctional compounds are described.

Trans-Bis(acetylacetonato-O,O')(3-methylpyridine-N)nitrocobalt(III)

The crystal structure determination of the title compound, [Co(C5H7O2)2(C6H7N)(NO2)], shows that the coordination geometry around the CoIII atom is slightly distorted octahedral with a Co—NO2 bond distance of 1.905 (3) Å. The crystal is photostable, which may be due to the narrow cavity around the nitro group.

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the thermal decomposition of dinitramide in aqueous solutions of HNO3, in anhydrous acetic acid, and in several other organic solvents were studied. The rate of the decomposition of dinitramide in aqueous HNO3 is determined by the decomposition of mixed anhydride of dinitramide and nitric acid (N4O6) formed in the solution in the reversible reaction. The decomposition of the anhydride is a reason for an increase in the decomposition rates of dinitramide in solutions of HNO3 as compared to those in solutions in H2SO4 and the self-acceleration of the process in concentrated aqueous solutions of dinitramide. The increase in the decomposition rate of nondissociated dinitramide compared to the decomposition rate of the N(NO2)2− anion is explained by a decrease in the order of the N−NO2 bond. The increase in the rate constant of the decomposition of the protonated form of dinitramide compared to the corresponding value for neutral molecules is due to the dehydration mechanism of the reaction.

Decomposition of 5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO): Energetics Associated with Several Proposed Initiation Routes

Initial steps for several proposed decomposition mechanisms of NTO have been studied theoretically in order to determine the energies of various reaction intermediates. The methods applied were restricted Hartree−Fock self-consistent field (SCF), single- and double-excitation configuration interaction (CISD), CISD corrected for unlinked quadruple excitations (CISD+Q), and coupled cluster including all single and double substitutions (CCSD) with a double-ζ plus polarization (DZP) basis set. Harmonic vibrational frequencies were computed to characterize the species at the stationary points. The previously reported mechanisms examined include decomposition initiated by C−NO2 homolysis, migration of ring substituents, and ring-opening processes. On the basis of the energetics of the various schemes, our computations suggest that C−NO2 bond homolysis is the most probable initial step for unimolecular decomposition of NTO.

Theoretical Study on Pyrolysis and Sensitivity of Energetic Compounds. Part I: Simple model molecules containing NO2 Group

AbstractUHF (Unrestricted Hartree‐Fock) Molecular Orbital calculations have been first performed for studying the pyrolysis mechanism of five compounds (nitromethane, methyl nitrate, nitroamine, methyl nitroamine and dimethyl nitroamine) containing NO2 group as the simple models of organic explosives by using PM3 and AM1 methods. The potential energy curves and activation energies of the five pyrolysis reactions (into radicals) have been obtained. The activation energies are consistent with the experimental impact sensitivity of these three kinds of explosives: C‐nitro < N‐nitro < O‐nitro compounds. It is found that there is a parallel linear relationship between the bond orders of NNO2 bond in the molecules of three nitroamine compounds and the activation energies of their initiation reactions breaking NNO2 bond. The obtained correlation coefficients between bond orders and activation energies from PM3 and AM1 calculations are 0.9962 and 0.9999, respectively.

Ab Initio Study of RDX Decomposition Mechanisms

The mechanism of the gas phase unimolecular decomposition of hexahydro-1,3,5,-trinitro-1,3,5,-triazine (RDX) has been investigated using first principles gradient-corrected density functional theory. We have calculated the potential energy profile for two previously suggested dissociation channels: (I) N−NO2 bond rupture, and (II) concerted ring fission to three methylenenitramine molecules. The activation barriers for channels I and II are predicted to be 34.2 and 52.5 kcal/mol at the B-PW91/cc-pVDZ level, respectively. We have performed a simple transition state theory analysis which indicates that the prefactors for channel I and II are roughly 7 × 1017 and 1 × 1017 s-1, respectively. Thus, our results suggest that path I is the dominant channel in gas phase thermal RDX decomposition.

Mass Spectral Fragmentation Pathways in 1,3,3-Trinitroazetidine

The electron impact (EI) fragmentation pathways of 1,3,3-trinitroazetidine (TNAZ) along with some 15N and 2H analogs were studied. Collision-induced dissociation was also used to investigate important peaks in the EI spectra. Isotopically labeled compounds allowed the determination of most of the major fragmentation peaks. It was found that the major pathway involves the loss of NO2 or HNO2 from the dinitroalkyl group followed by a loss of NO2 or NO from the nitramine group. The peak at m/z 46, [NO2]+, the base peak, resulted primarily from N—N bond scission while the peak at m/z 30, [NO]+, was equally likely to come from any NO2 bond. The fragmentation pathway of TNAZ showed similarities with other nitramine and nitrocarbon explosives. © 1997 by John Wiley & Sons, Ltd.

Zur Energiedelle von Diradikalen, VI. Das Energieprofil der NO2‐Addition an konjugierte Doppelbindungen: Eine Reaktion mit negativer Aktivierungsenergie

On the Energy Well of Diradicals, VIPart V: Ref. [1] . – The Energy Profile for the NO2‐Addition to Conjugated Double Bonds: A Reaction with Negative Activation Energy From the NO and temperature dependence of the reaction rates of 1,3‐butadiene, styrene, and methylenebenzocyclobutene with NO2 in the presence of NO, the energy profiles for the formation of the primary adducts are derived, which explain the inverse temperature dependence for the disappearance of the substrate at low NO concentrations and allow to calculate the bond strength of the C–NO2 bond (57.9 ± 1.3 kcal · mol−1).

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.

Studies on kinetics and mechanism of initial thermal decomposition of nitrocellulose

The thermal decomposition of nitrocellulose (NC) 12.1% N, has been studied with regard to kinetics, mechanism, morphology and the gaseous products thereof, using thermogravimetry (TG), differential thermal analysis (DTA), IR spectroscopy, differential scanning calorimetry (DSC) and hot stage microscopy.The kinetics of the initial stage of thermolysis ofNC in condensed state has been investigated by isothermal high temperature infrared spectroscopy (IR). The decomposition ofNC in KBr matrix in the temperature range of 142–151°C shows rapid decrease in O−NO2 band intensity, suggesting that the decomposition of NC occurs by the rupture of O−NO2 bond. The energy of activation for this process has been determined with the help of Avrami-Erofe'ev equation (n=1) and is ≈188.35 kJ·mol−1. Further, the IR spectra of the decomposition products in the initial stage of thermal decomposition ofNC, indicates the presence of mainly NO2 gas and aldehyde.

Darstellung von Mononitropentahydrohexaborat(2-) und Kristallstruktur von M2[B6H5(NO2)], M = K, Cs / Preparation of Mononitropentahydrohexaborate(2—) and Crystal Structure of M2[B6H5(NO2)], M = K, Cs

By electrochemical oxidation of [B6H6]2- in the presence of nitrite ions and the base DBU in dichloromethane solution mononitropentahydrohexaborate [B6H5(NO2)]2- ions are formed and can be isolated by ion exchange chromatography on diethylaminoethyl cellulose. The crystal structures of the K and Cs salt were determined from single crystal X-ray diffraction analyses. K2[B6H5(NO2)] is monoclinic, space group P21/m with a = 5.953(1), b = 8.059(4), c = 8.906(1) Å, β = 109.553(9)°; Cs2[B6H5(NO2)] is monoclinic, space group P21/a with a = 9.438(6), b = 9.644(7), c = 11.138(9) Å, β = 101.44(9)°. The B6 octahedron is compressed in the direction of the B—NO2 bond by about 5%, with bond lengths between 1.67 and 1.77 A.

Molecular orbital studies of the thermal decomposition mechanism of dimethylnitramine

AbstractThe electronic structures of dimethylnitramine (DMNA) were calculated using ab initio Gaussian 80 program at the Hartree‐Fock level with STO‐3G and STO‐4‐21G basis set, respectively. The Mulliken bond order of the NNO2 bond is the least one in comparision with those of the other bonds in the DMNA molecule. Two potential energy curves along the NN bond splitting pathway (RNN) were obtained using MINDO/3 and MNDO methods, respectively. These curves have the same trend and are qualitatively consistent with the results obtained from the thermolysis of nitromethane (CH3NO2). It was found that the frontier MO levels and the net charges of groups are changed with RNN distance. The products of thermal decomposition and the energy changes were calculated by MINDO/3 method and are discussed in this paper.

The thermal decomposition of peroxyacetic nitric anhydride (PAN) and peroxymethacrylic nitric anhydride (MPAN)

AbstractThe rate coefficients of thermal decomposition of peroxyacetic nitric anhydride (PAN) and peroxymethacrylic nitric anhydride (MPAN) were measured over the temperature range 302–323 K. The resulting Arrhenius expressions were k = 1017.4±0.4 exp(−28.5 ± 0.5/RT) for PAN, and k = 1016.2±0.7 exp(−26.8 ± 1.0/RT) for MPAN, where the activation energy is in Kcal/mol. These results are in good agreement with previous studies of PAN and other PAN‐type compounds, and imply that energies of RC(O)OONO2 bonds are relatively independent of the nature of R.

Reaction of N-aryl- and N-alkyl-benzimidoyl chlorides with silver nitrate

N-Arylbenzimidoyl chlorides, in which the N-aryl group is unsubstituted at the ortho- and para-positions, react with AgNO3 to yield N-(nitroaryl)benzamides in which the NO2 group resides in the ortho- or para-position. N-Arylbenzimidoyl chlorides, in which the N-aryl ring is 2,4,6-trisubstituted, react with AgNO3 to yield the corresponding N-aryl-N-nitrobenzamides. The formation of both types of product can be explained by the intermediacy of an O-nitro imidate. Spectroscopic and chemical evidence is presented for the formation of this intermediate in the reaction of N-(2,4,6-trisubstituted phenyl)benzimidoyl chlorides with AgNO3. Rearrangement of the O-nitro imidate is unimolecular and intramolecular. The rate of rearrangement is independent of the substituent in the C-aryl ring, but increases with the electron-withdrawing ability of the substituents in the N-aryl ring. A mechanism is proposed in which the imidoyl chloride reacts with AgNO3 to produce first a nitrilium ion which goes on to form an O-nitro imidate that subsequently rearranges via a homolytic cleavage of the O–NO2 bond. The ortho:para ratios of N-(nitroaryl)benzamides obtained in the present work indicate that O-nitro imidates are not responsible for the high ½ortho:para ratios sometimes observed in the nitration of anilides.

A b i n i t i o multiple reference double-excitation configuration-interaction ground and excited state potential curves for nitromethane decomposition

Reliable ab initio quantum chemical calculations for the ground and electronically excited potential energy surfaces for C–NO2 bond dissociation pathways in addition to the bond dissociation energy from the ground electronic state are crucial to evaluating energetic materials. The excited electronic state potential energy surfaces are important especially for laser induced decomposition. The curve crossings and avoided crossings are important since they determine the electronic states of the resulting fragments which influences their subsequent reactivities. We have carried out large basis set multiple reference double-excitation configuration-interaction (MRD-CI) calculations for the lowest several singlet and triplet potential curves for the H3C – NO2 decomposition of nitromethane. The proper ground state decomposition should lead to two radicals. The self-consistent-field (SCF) treatment (for the ground electronic state) was found to be satisfactory around the equilibrium structure (except for the ever-present ππ* transition of the electrons in the NO2 group) while failing completely to predict the proper dissociation limit. The analysis of the MRD-CI wave function allows distinguishing of two regions which can be interpreted as interaction within bonded molecule and interaction between species of already dissociated molecule.

Thermal decomposition of chlorofluoromethyl peroxynitrates

AbstractThe thermal decomposition of CCl3O2NO2,CCl2FO2NO2, and CClF2O2NO2 was studied in a temperature‐controlled 420 l reaction chamber using in situ detection of peroxynitrates by long‐path IR absorption. The temperature dependence of the unimolecular dissociation rate constants was determined at total pressures of 10 and 800 mbar in nitrogen as buffer gas, and the pressure dependence was measured at 273 K between 10 and 800 mbar. In Troe's notation, the data are represented by the following values for the limiting low and high pressure rate constants k0/[N2] and k∞ and the fall‐off curvature parameter Fc (in units of cm3 molecule−1 s−1, s−1): CCl3O2NO2,k0/[N2] = 6.3 × 10−3 exp(−85.1 kJ · mol−1/RT), k∞ = 4.8 × 1016 exp(−98.3 kJ · mol−1/RT), Fc = 0.22; CCl2FO2NO2, k0/[N2] = 1.01× 10−2 exp(−90.3 kJ · mol−1/RT), k∞ = 6.6 × 1016 exp(−101.8 kJ · mol−1/RT), Fc = 0.28; and CClF2O2NO2, k0/[N2] = 1.80 × 10−3 exp(−87.3 kJ · mol−1/RT), k∞ = 1.60 × 1016exp(−99.7 kJ · mol−1/RT), Fc = 0.30. From these dissociation rate constants and recently measured rate constants for the reverse reaction (see Caralp, Lesclaux, Rayez, Rayez, and Forst [19]), bond energies (=ΔH) of 100, 103, and 104 kJ/mol were derived for the RO2–NO2 bonds in CCl3O2NO2, CCl2FO2NO2, and CClF2O2NO2, respectively. The kinetic and thermochemical parameters of these decomposition reactions are compared with those of the dissociation of other peroxynitrates. Atmospheric implications of the thermal stability of chlorofluoromethyl peroxynitrates are briefly discussed.

Theoretical studies on structure‐property relationships of cellulose and nitrocellulose: I. Conformation, stability and conductivity

AbstractThe banding and electronic structures of a series of long‐chain macromolecules of cellulose, 2‐, 3‐, 6‐mononitrocellulose, 2,3‐,2,6‐, 3,6‐dinitrocellulose and trinitrocellulose as well as their structural units (i.e. single‐, double‐ or three‐ring systems) have been calculated by both the EH and CNDO/2 methods. The increase of molecular total energies is consistent with the decrease of their stabilities at the three conformations of gg, gt and tg. The Mulliken bond order of O—NO2 bond is the smallest in each molecule at any of the three conformations, which indicates that this bond is the weakest, and supports the view of initial homolytic cleavage of O—NO2 bond on slow thermal decomposition. The band gap at the edge of the first Brillouin zone far surpasses 5 eV for cellulose, and is less than 3 eV for mono‐, di‐, and trinitrocellulose. The results show that cellulose is a typical insulator, as we know, and it can be predicted that nitrocellulose has electric conductivity similar to that of semiconductor.