Structure and stability of isoxazoline compounds

Structure of isoxazoline compounds formed via the reaction of alkyl-substituted benzonitrile oxides with ethylene was determined by X-ray diffraction method. Isoxazoline ring is flattened, the bond lengths in it depend slightly on the nature of substituents (CH₃, C₂H₅) and their position in the benzene ring and the angle of rotation relative to the isoxazoline ring. The connection N-O has a length 1.422 Å. Thermal decomposition of isoxazolines in a liquid phase (160–280°C) is accompanied by the release of acetaldehyde and aromatic nitrile. Both the structure of the cycle and its stability is practically independent of the structure of an aromatic substituent. The rate constant of the initial stage is characterized by the low significance of kinetic parameters, E = 104°8 kJ mol^?1 and log a(A/c) = 7.2±0.8. The results obtained are rationalized in terms of biradical mechanism of isoxazoline ring-opening that includes an efficient recombination of the biradical and its disappearance as a result of synchronous multi-center rearrangement with the release of acetaldehyde.     

Five-membered 2,3-dioxo heterocycles: XCI. Reaction of 3-aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones with dimedone. Crystalline and molecular structure of 3′-benzoyl-4′-hydroxy-1′-(2-hydroxyphenyl)-6,6-dimethyl-6,7-dihydrospiro[1-benzofuran-3,2′-pyrrole]-2,4,5′(1′H,5H)-trione

3-Aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones reacted with 5,5-dimethylcyclohexane-1,3-dione to give 3′-aroyl-4′-hydroxy-1′-(2-hydroxyphenyl)-6,6-dimethyl-6,7-dihydrospiro[1-benzofuran-3,2′-pyrrole]-2,4,5′(1′H,5H)-triones. The crystalline and molecular structures of 3′-benzoyl-4′-hydroxy-1′-(2-hydroxyphenyl)-6,6-dimethyl-6,7-dihydrospiro[1-benzofuran-3,2′-pyrrole]-2,4,5′(1′H,5H)-trione were determined by X-ray analysis.     

Crystal structure of 4,4″-dinitro-[3,3′,4′,3″]-tris-[1,2,5]-oxadiazole

The crystal structure of a new energetic compound of 4,4″-dinitro-[3,3′:4,3″]-tris-[1,2,5]-oxadiazole is studied.     

Effect of low-temperature annealing on the magnetization curve of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + <Emphasis Type="Italic">x</Emphasis></Subscript> ceramics

The effect of low-temperature annealing on the magnetization curve of YBa₂Cu₃O_{6 + x} ceramics in the superconducting state (x ≈ 0.9) is investigated. When the annealing time is fairly long, the field dependence of magnetic moment M exhibits a feature in the form of a plateau, where the value of M remains almost constant. The evolution of this feature in the magnetization curves of annealed samples with annealing time and temperature is studied. It is assumed that low-temperature annealing gives rise to metastable ferromagnetic clusters in YBa₂Cu₃O_{6 + x} ceramics, the contribution of which to the magnetic moment accounts for the feature in the magnetization curves of the annealed samples.     

Separation of 167Tm, 165Er and 169Yb from erbium targets irradiated by 60 MeV alpha particles

Journal of Radioanalytical and Nuclear Chemistry - Thin natEr2O3 targets were irradiated on cyclotron by 60&nbsp;MeV alpha particles. Thulium and ytterbium radioisotopes, formed during...     

Nonexistence of global solutions of the Cauchy problem for systems of klein–Gordon equations with positive initial energy

We study the Cauchy problem for systems of weakly coupled Klein–Gordon equations with dissipations. We prove a theorem on the nonexistence of global solutions with positive initial energy.     

Temperature–Frequency Dependence of the Dielectric Response in LuFe2O4 Multiferroics

Physics of the Solid State - The temperature–frequency spectra of the complex dielectric permittivity of the LuFe2O4 multiferroics have been studied in the temperature range 100–400 K...     

Pretransition Phenomena Near First-Order Phase Transitions in Ion-Molecular Crystals

Physics of the Solid State - Processes of molecular relaxation in Li2SO4, Na2SO4, and K2SO4 sulfates; Li2CO3, Na2CO3, and K2CO3 carbonates; NaClO4 and KClO4 perchlorates; and Ca(NO3)2, Sr(NO3)2,...     

Structural and dynamic microheterogeneity of rubber powder

Spin probe EPR spectroscopy was used to study the local dynamics of vulcanizates of an ethylenepropylene-diene elastomer and rubber powders prepared from them. It was revealed that the preparation of rubber powders is accompanied by the formation of a polymer network with an essentially nonuniform local structure.