Effect of the molecular structure on the strength of the C-NO<Subscript>2</Subscript> bond in a series of monofunctional nitrobenzene derivatives

Geometric parameters and formation enthalpy and the enthalpy of the radicals formed during the homolytic breakage of C-NO₂ bond in 37 aromatic nitro compounds were calculated using different bases of the hybrid density functional method B3LYP, as well as the composite CBS-QB3 methods. On the basis of thermochemical data, were calculated the C-NO₂ bond dissociation energy and the activation energy of the radical gas-phase decomposition. Donor substituents were shown to cause an increase in the C-NO₂ bond dissociation energy, while the acceptors decrease it. The values of activation energies of gas-phase decomposition of aromatic nitro compounds calculated basing on the C-NO₂ bond dissociation energy are in good agreement with experiment.     

Quantum chemical studies on the structures, properties and decomposition of the azido derivatives of trinitrobenzenes

The geometries,heats of formation and electronic structures of 15 azido-derivatives of 1,2,3-TNB (Ⅰ),1,2,4-TNB (Ⅱ) and 1,3,5-TNB (Ⅲ) have been studied using quantum chemical AMI method at HF level.The effect of azido substitution on the structures and properties of TNBs has been discussed and the relative stability of the title compounds has been established.The processes of the decomposition of the title compounds by breaking C-NO2,C-N3 and CN-N2 bonds are investigated at UHF-AM1 level.It is shown that the decomposition of the title compounds may be initiated by the cleavage of both C-NO2 and N-N2 bonds.     

Kinetics of the thermal decomposition of α-polynitroalkyl sulfides and α-polynitroalkyl sulfones in the gaseous phase

Conclusions A study has been made of the gas-phase decomposition of eight-polynitroalkyl Sulfides and-polynitroalkyl sulfones. Decomposition parameters have been estimated and a mechanism involving rupture of the C-NO₂ bond has been established. Substitution of a S atom in the position to the NO₂ group lowers the C-NO₂ bond energy by R10 kcal/mole.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 310–312, February, 1977.     

Spectroscopic and Thermal Studies on 2,4,6-trinitro Toluene (TNT)

The kinetics and mechanism of the initial stage of thermal decomposition of 2,4,6-trinitro toluene (TNT), a widely used high explosive, have been studied, together with its morphology and evolved gaseous products using thermogravimetry (TG), differential thermal analysis (DTA), infrared spectroscopy (IR) and hot-stage microscopy. The kinetics of the thermolysis has been followed by IR after suppressing volatilisation by matrixing and by isothermal TG without suppressing volatilisation to simulate actual user conditions. The best linearity was obtained for Avrami-Erofeev equation for n=1 in isothermal IR and also in isothermal TG. The activation energy was found to be 135 kJ mol⁻¹, with logA (in s⁻¹) 12.5 by IR. The effect of additives on the initial thermolysis of TNT has also been studied. Evolved gas analysis by IR showed that CO₂, NO₂, NO and H₂O are more dominant than N₂O, HCN and CO. The decomposition involves the initial rupture of the C-NO₂ bond, weakened by hydrogen bonding with the labile hydrogen atom of the adjacent CH₃ group, followed by the abstraction of the hydrogen atom of the methyl group by NO₂, generated in the initial step. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of the simultaneous presence of nitro and amine substituents in cubane and some azacubanes

We have carried out an ab initio self-consistent-field molecular orbital study of the structures and bond orders (as measures of relative bond strengths) of nitro and aminonitro derivatives of cubane and some azacubanes. The NO₂ group is found to have, in general, a conformation-dependent effect on relative bond strengths. When the plane of the nitro group is perpendicular to that of an endocyclic bond, that bond is weakened. An aza nitrogen adjacent to C-NO₂, however, eliminates the bond-weakening due to a perpendicular nitro group, except when a C-NH₂ is also adjacent to the C-NO₂. The NH₂ group has a direction-specific bond-weakening effect on one [and only one] endocyclic bond; the particular bond undergoing this weakening is determined by the orientation of the amine nitrogen lone pair. The influences of the NO₂ and NH₂ are essentially independent; when these substituents are on adjacent carbons the effects are reinforcing. Thus, the combination of a perpendicular NO₂ and an NH₂ on adjacent carbons in cubane and azacubanes produces a marked bond weakening. Our findings suggest that strained cage systems that have alternating aza nitrogens and C-NO₂ groups should be further investigated as potential high-energy systems.     

Thermal behavior of copper(II) 4-nitroimidazolate

The thermal behavior of copper(II) 4-nitroimidazolate (CuNI) under static and dynamic states are studied by means of high-pressure DSC (PDSC) and TG with the different heating rates and the combination technique of in situ thermolysis cell with rapid-scan Fourier transform infrared spectroscopy (thermolysis/RSFTIR). The results show that the apparent activation energy and pre-exponential factor of the major exothermic decomposition reaction of CuNI obtained by Kissinger’s method are 233.2 kJ mol⁻¹ and 10^17.95 s⁻¹, respectively. The critical temperature of the thermal explosion and the adiabatic time-to-explosion of CuNI are 601.97 K and 4.4∼4.6 s, respectively. The decomposition of CuNI begins with the split of the C-NO₂ and C-H bonds, and the decomposition process of CuNI under dynamic states occurs less readily than those under static states because the dynamic nitrogen removes the strong oxidative decomposition product (NO₂). The above-mentioned information on thermal behavior is quite useful for analyzing and evaluating the stability and thermal charge rule of CuNI.     

Computational study on energetic properties of nitro derivatives of furan substituted azoles

Density functional theory has been used to investigate geometries, heats of formation (HOFs), C-NO₂ bond dissociation energies (BDEs), and relative energetic properties of nitro derivatives of azole substituted furan. HOFs for a series of molecules were calculated by using density functional theory (DFT) and Møller–Plesset (MP2) methods. The density is predicted using crystal packing calculations; all the designed compounds show density above 1.71 g/cm³. The calculated detonation velocities and detonation pressures indicate that the nitro group is very helpful for enhancing the detonation performance for the designed compounds. Thermal stabilities have been evaluated from the bond dissociation energies. Charge on the nitro group was used to assess the impact sensitivity in this study. According to the results of the calculations, tri- and tetra-nitro substituted derivatives reveal high performance with better thermal stability.     

Vapour-liquid equilibrium measurements for binary mixtures of R32, R143a, R134a and R125 with a perfluoropolyether lubricant

In the present work, vapour-liquid equilibria of four binary systems refrigerant-lubricant oil have been investigated, CF₃CHF₂ (R125), CF₃CH₂F (R134a), CF₃CH₃ (R143a) and CH₂F₂ (R32) as refrigerants and a commercial perfluoropolyether (PFPE), Fluorolink D10H, as lubricant. Vapour-liquid equilibrium data, consisting of isothermal measurement of equilibrium pressure at a fixed composition, have been correlated with an extended Flory-Huggins equation and the corresponding parameters have been determined. Good agreement has been found between experimental data and the model predictions.     

Dissociation energy of the C-NO2 bond in 2-nitrofuran

Conclusions The dissociation energy of the C-NO₂ bond in 2-nitrofuran is 70.4 kcal/mole.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 678–679, March, 1987.     

Cyclization of polyfluoro substituted 2-amino- and 2-acetylaminodiaryl ethers into derivatives of phenoxazine

Cyclization of the diaryl ethers 4-RC₅F₄OC₆H₄NH₂(NHAc)-2 (R=C-NO₂, C-CF₃, N), containing an electron accepting group in the fluorinated ring, proceeds in DMF in the presence of K₂CO₃ following a Smiles rearrangement.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 846–849, April, 1990.     

Examples of the application of titration techniques in the process industry

Different titration techniques are used for analyses of the nitrating acids in three different industrial processes, namely in the production of glycerol trinitrate (nitrate ester,  C-ONO₂), trinitrotoluene (nitro group,  C-NO₂) and trimethylene trinitramine (nitramine, N-NO₂). The determination of the composition of the process acids, which consist mainly of water, nitric acid, sulphuric acid, acetic acid and hexamethylenetetramine with minor amounts of nitrous acid and ammonium nitrate, are complicated by the ability of the process acids to dissolve the product to various extents. Acid-base titrations as well as oxidation-reduction titrations and voltammetry are used to provide a rapid system for analysing the process acids.     

Crystal Structure of 1-nitro-2-phenylcycloprop-2-enecarbonitrile

The synthesis and x-ray crystal structure of 1 -nitro-2-phenylcycloprop-2-enecarbonitrile [1] is reported. The C-NO₂ bond length in1 is similar to but slightly shorter than that reported for 1, 2-diphenyl-3-nitrocyclopropene (2). Unlike2, 1 shows no tendency to ionize to the corresponding cyclopropenium ion in solution. This result is further supported by ab initio calculations.     

A computational study of some nitrofluoromethanes

A group of eight nitrofluoromethanes has been studied by the ab initio SCF GAUSSIAN 82 computational procedure. All structures were optimized at the 3-21G level and then used to compute bond orders, as measures of relative bond strengths, and electrostatic potentials, as guides to the molecular charge distributions. The C-F bonds were found to be strengthened by the presence of other fluorines or nitro groups; this is attributed to inductive electron withdrawal by these other substituents, which leads to significant double-bond character in the C-F bond, through resonance back-donation by the fluorine. This simultaneously weakens or even eliminates the negative electrostatic potential normally associated with the fluorine. The interesting observation that there are marked differences between the strengths of the two N-O bonds in some nitro groups can be quantitatively related to the environment of each oxygen. The C-NO₂ bond strengths are relatively insensitive to the presence of other-NO₂or-F substituents. However, CHF(NO₂)₂ is found to be significantly more stable than CH(NO₂)₃, presumably because the crowding of three -NO₂ groups together on the same carbon is partially relieved.     

Molecular structures of mononitroanilines and their thermal decomposition products

The molecular structures of 2-nitro, 3-nitro, and 4-nitroaniline and their internal rotational isomers were calculated by anab-initio method using HF/6-31G* basis set. The geometries were influenced by the nitro group's position. The perturbation of the amino group on the nitro group was observed in a 2-nitroaniline isomer having a molecular structure distinct from that of the other two isomers. Among them, 4-nitroaniline is the most stable one. Internal rotation tests of either the nitro or amino group of 3-nitro and 4-nitroaniline indicate that no significant deformations of the phenyl ring occurred after internal rotation; however, the internal rotational isomers of 2-nitroaniline differed from its original structure. Relatively easier internal rotation of the nitro group than the amino group and different C-NO₂ and C-NH₂ bonds indicate the bond-breaking message of nitroanilines. As products of explosives induced by thermal or shock are of interest, five products of 2-nitroaniline were selected to assess their geometries and energies. The above calculations revealed that these products are thermodynamically unfavorable.     

Disproportionation of triorganotin species,R3SnX

Triorganotin compounds, R₃SnX, have found extensive use as a biological agents in such areas as agrochemicals, marine antifoulants and timber preservatives. In contrast, di(R₂SnX₂) and tetraorganotin derivatives (R₄Sn) possess less biological activity than do their triorganotin counterparts. It has been shown that disproportionation of R₃SnX species (i.e. to produce R₂SnX₂ and R₄Sn) can occur especially when X is a chelating or bridging group such as oxide, carboxylate, hydroxy ketone or hydroxyquinoline. This process has implications for the industrial applications and analysis of R₃SnX compounds.     

Thermal analysis of cobalt,nickel and copper complexes of 2-aminothiazole

The thermal decomposition of 2-aminothiazole (2-amt) complexes of general formula M(2-amt)₂X₂ [M = Co(II) and Cu(II)] and Ni(2-amt)₄X₂ [X = Cl and Br] have been studied in air and argon by TG and DTG as well as by DTA in nitrogen; end products from the decompositions in air have been characterised by X-ray powder diffraction. Decomposition stoichiometries have been proposed and factors governing the thermal decomposition have been discussed.     

Synthesis and phase formation study in K2MoO4-SrMoO4-R2(MoO4)3 systems (where R = Pr, Nd, Sm, Eu, and Gd)

Subsolidus phase formation in K₂MoO₄-SrMoO₄-R₂(MoO₄)₃ systems, where R = Pr, Nd, Sm, Eu, and Gd, in which KSrR(MoO₄)₃ triple molybdates are formed and crystallize in monoclinic crystal system (space group P2₁/n), have been studied using X-ray powder diffraction, differential thermal analysis (DTA), and vibrational spectroscopy. Unit cell parameters have been determined for these molybdates; their IR and Raman spectra are reported.     

Stability of polynitropentanes

Conclusions The -nitro group in 1,3,5-polynitropentanes affects the reaction site located at the terminal carbon atom by a field effect mechanism as a consequence of steric approximation. As a result, the dissociation energy of the C-NO₂ bond is reduced by 20–30 kJ/mole.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2822–2824, December, 1984.The authors thank L. T. Eremenko and G. V. Oreshko for providing samples of the compounds studied.     

Ultrasonic velocity study of poly(R,R,4,4-cyclohexylidene diphenylene diphenyl ether-4,4-disulfonate) solutions at 30, 35 and 40 °C

Ultrasonic velocity (2 MHz) and acoustic parameters of poly(R,R^′-4,4^′-cyclohexylidene diphenylene diphenyl ether-4,4^′-disulfonate) (PS-1: RR^′H; PS-2: RCH₃ and R^′H; PS-4: RCH₃ and R^′Cl) solutions (chloroform, 1,2-dichloroethane and tetrahydrofuran (THF)) at 30, 35 and 40 °C have been determined to understand the effect of methyl and chlorine substituents on molecular interactions to support solvophilic or solvophobic nature of the polymers. The linear increase of U, Z, R, b, π, (α/f²)_Cl and τ with C and decrease of K_s, r, L_f and V_f with C suggested the existence of strong molecular interactions and hence solvophilic nature of the polymers, which is supported by positive values of S_n. A rise in temperature resulted in less ordered structure and more spacing between the molecules. The solvophilic nature of the polymers caused nonlinear variation of φ_v2 and φ_Ks with C and T. A powerful solvation exists in THF system. Structural modification is found above 2% for PS-2 and PS-4. The decrease of S_n with C and T indicated the presence of polymer-polymer interactions. The decrease of S_n with T is due to disruption of the structure formed by predominant thermal energy over molecular interaction energy.     

Investigation of solution and solid-state properties of poly(R,R,4,4-cyclohexylidene diphenylene diphenyl-4,4-disulfonate)

Solution and solid-state properties of poly(R,R^′,4,4^′-cyclohexylidene diphenylene diphenyl-4,4^′-disulfonate) (PS-6: R=R^′=H; PS-7: R=CH₃, R^′=H; PS-8: R=R^′=Cl; PS-9: R=CH₃, R^′=Cl and PS-10: R=R^′=Br) have been determined and discussed in terms of nature of the substituents. Ultrasonic velocity (2 MHz) and acoustical parameters of PS-7 and PS-9 solutions in chloroform, 1,2-dichloroethane and tetrahydrofuran (THF) at 30, 35 and 40 °C have been evaluated to understand the effect of methyl and chlorine groups, concentration, and temperature on molecular interactions. The data are interpreted in light of solvent-polymer and polymer-polymer interactions. Predominant solvation is observed in THF system and the least in chloroform system at all three temperatures. The structural change is observed above 2%. Both the polymers possess structure-forming tendency and it is supported by positive values of S_n.The densities of PS-7 and PS-9 determined by floatation method are in excellent agreement with calculated values but those determined by specific volume method differ remarkably from calculated values due to solvation effect. PS-7 and PS-9 possess respectively tensile strength of 38.4 and 1.1 N/mm²; electric strength of 16.2 and 25.0 kV/mm and volume resistivity of 5.7×10¹⁶ and 1.0×1017Ωcm. The low tensile strength of PS-9 is due to low molecular weight, rigid and brittle nature of the polymer chains. PS-6 to PS-9 are thermally stable up to about 349-379 °C while PS-10 up to about 279 °C and involved two-step degradation. DTA thermograms indicated T_g at about 204-226 °C. High activation energy indicated rigid nature of the polymer chains and the positive magnitudes of ΔS* indicated less ordered transition state. The nature of the substituents (CH₃, Cl and Br) affected thermal, mechanical and electrical properties.