Effects of Structural Factors in Silyl Ethers Derived from Terminal Acetylenic Alcohols on 1,4-O→Csp Migration of the Silyl Group

Effects of structural factors in silyl ethers derived from terminal acetylenic alcohols on 1,4-OC_sp migration of the silyl group in the Iotsitch reagent were studied. The effect of steric factor at the carbon atom neighboring to the reaction center was found to be stronger than that at the silicon atom in the migrating group.     

Mass-spectrometric determination of the tautomeric forms of alkyl(aryl) benzazolylazoketoximes

A mass-spectrometric study of a series of alkyl(aryl)benzazolylazoketoximes as compared with arylazoketoxime was made. The ratios of the tautomers (oxime nitroso) in the gas phase at the moment of vaporization of the samples were determined. It is shown that the ratios of the tautomers are determined by both the basicity of the heterocycle and the character of the substituent attached to the methylidyne carbon atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1506–1511, November, 1981.     

Determination of Triandrin and Salicin in Salix viminalis L. by Reversed-Phase High-Performance Liquid Chromatography

The optimal separation of phenolic components of the bark of basket willow Salix viminalis L. was attained using reversed-phase high-performance liquid chromatography with isocratic elution. Triandrin (1-O--D-glucopyranoside of p-coumaryl alcohol) and salicin (1-O--D-glucopyranoside of salicyl alcohol) were identified. Regularities in the retention of triandrin and salicin in the Separon SGX C₁₈–binary mobile phase (acetonitrile–water) system were considered. A procedure was developed for the quantitative determination of triandrin in raw basket-willow bark and its extract.     

Destruction of aspen wood by the fungusPhanerochaete sanguinea quantitative1H and13C NMR spectroscopies of biologically degraded lignin

The lignin of mechanically ground aspen wood and lignins isolated from aspen wood attacked by the fungusPhanerochaete sanguinea have been investigated by quantitative¹H and¹³C NMR spectroscopies. It has been shown that the biodestruction of the lignin takes place through the cleavage of alkyl-aryl and aryl-aryl bonds and is accompanied by demethylation (demethoxylation) reactions, and the oxidation of C and C atoms. In addition to reactions in which the C—C bonds are cleaved, the formation of ether bonds has been observed. An interconnection has been shown between the variations in the amount of functional groups, fragments, and the bonds in biolignins and the loss in mass of the wood. A method is proposed for evaluating the carbohydrate content in lignin preparations using the NMR method.Wood Chemistry Branch of the Institute of Organic Chemistry, Siberian Division of the Russian Academy of Sciences, Irkutsk. Irkutsk State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 547–557, July–August, 1994.     

Quantum-Chemical Modelling of the Electronic Structure and the Chemical Bond in Multiwalled Nanotubes Based on Metal Diborides

A quantum-chemical model of multiwalled nanotubes of magnesium diboride was produced. The electronic structure and the nature of the interatomic bonds in the multiwalled nanotubes were studied in relation to the diameter and the number of Mg-B₂ layers: (6,6) (3,3)@(6,6) (6,6)@(12,12) (3,3)@(6,6)@(12,12). Possible methods for the production of diboride nanotubes are discussed. Features of the electronic states in composite nanotubular structures based on the diborides of s and p metals are examined for the first time as illustrated by the (6,6)AlB₂(12,12)MgB₂ multiwalled nanotube.     

The first focus quantity of a complex monodromic singular point

We consider the problem of distinguishing the center and focus in the case of a strongly degenerate singular point. A sufficient condition is explicitly stated for the existence of a focus for singular points of vector fields on the plane belonging to a certain class.Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 13, pp. 106–122, 1988.     

Pressure effect onT c and resistivity: Localization in YBa2Cu3O x oxides

We have studied the effect of hydrostatic pressures up to 20 Kbar on the temperature dependence of the resistivity (T) and the effect of quasihydrostatic pressure up to 200 Kbar on the lattice parameters of YBa₂Cu₃O _x for different oxygen concentrations (x=6.95–6.2). Pressure produces a decrease of resistivity in normal state, an increase ofT _c , and a suppression of semiconducting-like resistivity (T) at lowx. The dependence of dT _c (x)/dP onx is nonmonotonic; the record values of dT _c /dP=(1.0±0.1) K/Kbar are observed forx=6.7 and 6.8. The derivative dln/dP atT=293 K differs by the factor 1.8 between superconducting and nonsuperconducting compounds. The compressibility and its pressure derivative alonga, b andc-directions in YBa₂Cu₃O _x have been determined. The most remarkable variation is alongc-direction. A nonmonotonic dependence of dk _c (x)/dP onx has been observed.The results are discussed in the context of localized effects in disordered oxygen-deficient YBa₂Cu₃O _x .     

New type of spin-labeled aminoenal

Ethynyl-substituted nitronyl nitroxide is involved in the 1,3-dipolar cycloaddition with cyclic nitrones without affecting the nitronyl nitroxide fragment. The reaction of 2,4,4,5,5-pentamethyl-4,5-dihydro-1H-imidazole 3-oxide produces the corresponding 1,2,3,7a-tetrahydroimidazo[1,2-b]isoxazole derivative. The analog of the latter derived from 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide is transformed into spin-labeled aminoenal. The solid phase of aminoenal is formed by packing unsymmetrical trimers resulting from the self-assembling of the molecular fragments based on a hydrogen bond network. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1975–1979, October, 2007.     

Reduction of nitro derivatives of 1,3,4-oxadiazole

A method for the synthesis of amino derivatives of 1,3,4-oxadiazole by the reduction of the corresponding nitro compounds with hydrazine hydrate in the presence of Raney nickel in dioxane-ethanolic solution has been developed.