The energies of dissociation of the N—O bonds in pyridine 1-oxide derivatives

The enthalpies of combustion of some pyridine derivatives in the solid state have been measured by precision bomb calorimetry, and their enthalpies of formation have been calculated. The enthalpies of sublimation of these compounds have been determined from the experimental temperature dependences of saturated vapor pressure using the Clausius-Clapeyron equation. The enthalpies of combustion, formation, and sublimation are the following (kJ mol^–1): -3360.9±2.1, -0.5±2.1, and 79.1±1.3, respectively, for 4-methylpyridine 1-oxide; -2551.0±1.7, 11.7±1.7, and 89.1±2.5, respectively, for 4-nitropyridine 1-oxide;-2355.6±1.3, 102.1±1.3, and 106.3±2.9 for 2,4,6-trinitropyridine 1-oxide; and -2287.6±1.3, 34.3±1.3, and 101.7±2.9 for 2,4,6-trinitropyridine. The enthalpies of formation in the solid state and the enthalpies of sublimation of pyridine derivatives obtained together with the literature data allowed the energies of dissociation of the donor-acceptor N—O bonds in pyridine 1-oxides to be calculated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 660–662, April, 1995.     

Synthesis of aromatic derivatives of 1,5-benzodiazepine in the reaction of 4-nitro-o-phenylenediamine with chalcone dibromides

The reaction of 4-nitro-o-phenylenediamine with 4-nitro-4-R-chalcone dibromides affords the corresponding -(2-amino-4-nitroanilino)chalcones; x-ray diffraction data indicate that these are the Z-isomers. Experiments have been perfortned to determine the conditions required for cyclization of these compounds into 2, 4-diaryl7(8)-nitro-1, 5-benzodiazepines. In the solid phase or in ethanol solutions, these latter compounds exist primarily in the 3H tautomeric form; but in DMSO solutions, the 1H form predominates.Khar'kov State University, Khar'kov 310077. Institute of Heteroorganic Chemistry, Russian Academy of Sciences, Moscow 117813. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 950–958, July, 1995. Original article submitted June 30, 1994; revision submitted April 3, 1995.Deceased     

Nitroazines. 19. Prototropic tautomerism in 6-nitro-7-oxo-4,7-dihydro-1,2,4-triazolo[5,1-c][1,2,4]triazines

Prototropic reactions of 6-nitro-7-oxo-4,7-dihydro-1,2,4-triazolo[5,1-c][1,2,4]triazines is tautomeric as established from photoionization results. The ratios of the tautomers in the gas phase and in solution have been determined by mass and ¹³C NMR spectroscopy.For Communication 18 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1555–1559, November, 1992.     

Maps of intragranular precipitation strengthening

Maps of strengthening by small (semi)coherent precipitates homogeneously dispersed in the grains have been constructed. They can show the most probable dislocation-particle interaction mechanism and the strengthening effect of a given dispersion of particles. As an application, the effect of-Ni₃(Al, Ti) and M₂₃C₆ precipitation in austenitic steels is discussed.     

Cyclocondensation of 2-Aminobenzimidazole with Dimedone and Its Arylidene Derivatives

The reactions of 2-aminobenzimidazole with substituted benzaldehydes and dimedone, 2-arylidene derivatives of dimedone, 9-arylhexahydro-1H-xanthene-1,8(2H)-diones and also with dimedone and DMF have been studied. The direction of formation of the pyrimidine ring has been established and discussed. An X-ray structural investigation of 2,2-dimethyl-2,3-dihydrobenzimidazo[1,2-a]quinazolin-4(1H)-one has been carried out.     

Infrared absorption and electron paramagnetic resonance studies of vinyl radical in noble-gas matrices

Vinyl radicals produced by annealing-induced reaction of mobilized hydrogen atoms with acetylene molecules in solid noble-gas matrices (Ar, Kr, and Xe) were characterized by Fourier transform infrared and electron paramagnetic resonance (EPR) spectroscopies. The hydrogen atoms were generated from acetylene by UV photolysis or fast electron irradiation. Two vibrational modes of the vinyl radical (nu7 and nu5) were assigned in IR absorption studies. The assignment is based on data for various isotopic substitutions (D and 13C) and confirmed by comparison with the EPR measurements and density-functional theory calculations. The data on the nu7 mode is in agreement with previous experimental and theoretical results whereas the nu5 frequency agrees well with the computational data but conflicts with the gas-phase IR emission results.     

Reactions of 4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidines with α,β‐unsaturated carbonyl compounds

The reaction of 5,7‐diphenyl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidine ( 1 ) with α,β‐unsaturated carbonyl compounds 2a‐f led to the formation of the alkylated heterocycles 3a‐f (Figure 1). However, the reaction of 5‐methyl‐7‐phenyl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidine ( 5 ) with 2a‐c yielded under the same conditions the triazolo[5,1‐b]quinazolines 6a‐c (Figure 3). In this case, the alkylation is followed by a cyclocondensation. The structure elucidation of the products is based on ir, ms, ¹H and ¹³C nmr measurements and on an X‐ray diffraction study.     

Kinetic equations with a complex balanced stationary point

A class of ordinary differential equations including nonideal nonisothermal kinetics is introduced. The behavior of their solutions for the system with a positive complex-balanced stationary point is studied. Sufficient conditions for this point to exist are described.

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Mass spectra of methylsubstituted monosila- and monogermacyclobutanes, 1,2- disila- and 1,2-digermacyclopentanes. Some correlations with thermal decomposition

The mass spectra of 1,1-dimethyl-1-silacyclobutane (I—as reported by Cherniak et al.),⁶, 1,1-dimethyl-1-germacyclobutane (II), 1,1,2,2-tetramethyl-1,2-disilacyclopentane (III) and 1,1,2,2-tetramethyl-1,2-digermacyclopentane (IV) are compared and some correlations between electron-impact fragmentation and thermal decomposition are derived. The mass spectra of the germanium compounds with respect to the silicone compounds are enriched by light fragment ions and exhibit lower intensities of odd-electron ions. The composition of some ions and apparently of neutral fragments coincides with that of the unstable intermediates which are suggested in the thermal decomposition mechanism of some related compounds. The loss of C₂H₄ is more characteristic under electron-impact as well as in thermal decomposition of Si-compounds, while C₃H₆ is preferable eliminated by the Ge-compounds.