Kinetics of Reaction between Superoxide Anion and Propyl Bromide

Russian Journal of Organic Chemistry -     

Dynamics of a magnetized relativistic electron beam in composite drift tubes with virtual cathodes

A computer simulation of the dynamics of a magnetized electron beam in composite drift tubes with multiple virtual cathodes is presented. For a single-cavity tube, the value of the limiting current is found to equal that given by an exact formula. For two-and three-cavity tubes, it is revealed that the values of the limiting currents are smaller than those reported previously and that the current diagram may have a different structure. These phenomena are attributed to Pierce instability. The efficiency of microwave generation as a function of injection current is examined. It is established that the efficiency is minimum if the current equals any of the limiting values refined.     

Heat capacity and thermodynamic functions of 4,4′-dimethylbiphenyl and 4,4′-di-tert-butylbiphenyl

The heat capacity (C _{p m} ) of 4,4′-dimethylbiphenyl and 4,4′-di-tert-butylbiphenyl in the temperature range of 8—373 K was measured by low-temperat ure adiabatic calorimetry, and thermodynamic characteristics of the solid-phase transitions of 4,4′-d i-tert-butylbiphenyl were determined. Temperatures, enthalpies, entropies of melting, and the purity of the samples of the tested substances were determined by means of differential scanning calorimetry. The main thermodynamic functions of the substances in the condensed state at 298 K were calculated.     

Study of thermal stability of tetraarenoporphyrazine metal complexes

Thermal stability in air of metal complexes of certain tetraarenoporphyrazines: tetrapyrazineporphyrazine, tetra-2,3-quinoxalinoporphyrazine, and tetra-2,3-naphtholocyanine, and also of copper complexes of tetra(tert-butyl)phthalocyanine, tetrapyrazineporphyrazine, and tetra-2,3-quinoxalinoporphyrazine substituted at the periphery was studied for the first time by the methods of thermogravimetry and differential thermal analysis. The effective thermal oxidation of these compounds occurs in the interval 620–820 K, and the tolerance for it is determined by both the metal nature and the structure of the macrocyclic ligand periphery.     

Thin-layer chromatographic analysis of the products of the hydrogenation of anabasine,ammodendrine, and isoammodendrine

Chemistry of Natural Compounds - It has been shown by TLC on a nonfixed layer of Al2O3 that the hydrogenation ofl-anabasine forms four stereoisomers and that of N-acetylanabasine three substances,...     

Process of magnetic field penetration into the high-temperature superconductor YBa2Cu3O7−δ

The processes of magnetic field penetration into the ceramic samples of the HTSC YB₂Cu₃O_～6.95 at T<T _c are studied by the methods of internal friction and magnetization measurements. A clearly manifested correlation is observed between the field dependences of the internal friction spectrum parameters (the logarithmic damping decrement Q ^?1 and the resonance frequency f) and the trapped magnetic flux ΔM. The magneto-mechanical approach we used reveals a significant difference in the field dependences of the densities of pinned (N _p) and free (N _f) Abrikosov vortices for H>H _c1.     

Synthesis and properties of lanthanide complexes with tetrapyrazinoporphyrazine and its substituted derivatives

Reactions of dicyanopyrazine and its tert-butyl-, diphenyl-, and dipyridyl-substituted derivatives with erbium, thulium, ytterbium, and lutetium chlorides, acetates, and acetylacetonates gave the corresponding tetrapyrazinoporphyrazine metal complexes which were characterized by elemental analyses, and IR, ¹H NMR, and electronic absorption spectra. The stability of the complexes to thermooxidative decomposition in air was also studied.     

Phase separation in La1−x Sr x CoO3 solid solutions with a perovskite structure

The properties of La_1−x Sr _x CoO₃ (x = 0, 0.15, 0.20, 0.30) solid solutions are investigated using neutron diffraction, positive-muon spin relaxation (precession) measurements, and extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy. The results obtained are interpreted within the model of phase separation into ferromagnetic regions enriched with Sr²⁺ ions and nonmagnetic regions similar in composition to the LaCoO₃ compound.

     

Formation of a PIII−C(sp2) bond by addition of diphenyl(trimethylsilyl)phosphine to activated acetylenes

Diphenyl(trimethylsilyl)phosphine reacts with alkoxy(alkyl)acetylenes to give mixtures of addition products, (2-alkoxy-2-trimethylsilylalkenyl)diphenylphosphines and (2-alkoxyalkenyl)diphenylphosphines. The reaction is sensitive to the solvent; in MeCN, it gives only nonsilylated products. (1-Alkoxyethenyl)diphenylphosphines were obtained as the main products upon the reaction of Ph₂PSiMe₃ with terminal alkoxyalkynes, irrespective of the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1792–1796, September, 1998.