Clathrate formation in the tetraisoamylammonium propionate-water system

In this paper we examine clathrate formation in the tetraisoamylammonium propionate-water binary system. We have found formation of four polyhydrates, two of which are metastable over the whole temperature range studied. All polyhydrate crystals were isolated and their compositions and densities determined; for (i-C₅H₁₁)₄NC₂H₅COO·36.5H₂O, unit cell parameters were additionally found. The results are compared with data for tetra-n-butylammonium carboxylate polyhydrates, and the structure of the title compounds is suggested. It is confirmed that the isoamyl radical stabilizes the tetradecahedral void of the clathrate hydrate framework better than the n-butyl radical. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 67–71, May–June, 1994. Translated by L. Smolina     

Use of X-ray diffraction data in stereochemical studies of (−)-menthone reactions with aromatic aldehydes

X-ray diffraction analysis proved that the stereochemical configuration of interaction products of (−)-menthone with aromatic aldehydes (α,β-unsaturated ketones or β-hydroxyketones) depends on the generation conditions of intermediate enolate carbanions. In irreversible deprotonation of (−)-menthone with strong sterically hindered organometallic bases, products of interaction with aldehydes preserve the 1R,4S-configuration; in equilibrium conditions, 1R,4R-diastereomers of the corresponding α,β-unsaturated ketones are formed with high stereoselectivity. Institute of Single Crystals, Academy of Sciences of Ukrainian Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 5, pp. 133–142, September–October, 1994. Translated by T. Yudanova     

Orbital electronegativity concept and its role in energetic crystal chemistry

Development of the orbital electronegativity concept since, 1934 is considered. It is shown that the concept is well substantiated from the quantum chemical viewpoint and is used in such fields of chemistry and crystal chemistry as the Lewis acid-base theory, the reactivity theory, etc. Its application is based on the electronegativity balance principle, which includes not only intraatomic effects but also different interatomic interaction contributions. The concept became a natural tool in modern methods for predicting and modeling the structure and properties of molecules and crystals. M. V. Lomonosov Moscow State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 1, pp. 111–127, January–February, 1994. Translated by L. Smolina     

Fluctuation conductivity in superconducting MgB2

According to the crystal structure of MgB₂ and band structure calculations, quasi-two-dimensional (2D) boron planes are responsible for the superconductivity. We report on critical-field and resistance measurements of 5.6-μm-thick MgB₂ films grown on a sapphire single-crystal substrate. Resistivity measurements yield a temperature dependence of the fluctuation conductivity above the critical temperature, which agrees with the Aslamazov-Larkin and Maki-Thompson theory of fluctuations in layered superconductors, indicating a quasi-two-dimensional nucleation of superconductivity in MgB₂.     

General base catalysis in the decomposition of N-Cl-Valine in aqueous solution

This article analyzes the kinetics of the decomposition of N-Cl-Valine in aqueous solution, which is formed rapidly by chlorination of Valine with sodium hypochlorite. A general-base catalyzed process not yet described is reported. The experimental evidence shows two competitive decomposition paths: an unimolecular concerted fragmentation process (k = (1.8 ± 0.1) · 10^?4 s^?1 at 298 K) and the other one is an E2 elimination process whose importance increases with pH and depends on the nature and the concentration of the bases present in the medium. © 1994 John Wiley & Sons, Inc.     

Modulation of Particle Concentrations in the Interference Laser Radiation Field

Spatial redistribution of microparticles in a suspension on exposure to the interference laser field depending on the parameters of the particles and the field characteristics has been analyzed theoretically. Results of experimental investigations are presented that illustrate the capture of an ensemble of polymeric small spheres and also of the lymphocytes of human blood and other microparticles in a liquid in the interference radiation bands of the He–Ne laser.     

Triangles of Minimal Perimeter Circumscribed about a Convex n-Gon

An algorithm for finding a circumscribed triangle of the minimal perimeter is suggested. Properties of such a triangle are described. Bibliography: 1 title.