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281.
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 相似文献
282.
L. A. Kutulya V. V. Vashchenko V. P. Kuznetsov E. E. Lakin 《Journal of Structural Chemistry》1994,35(5):688-696
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 相似文献
283.
V. S. Urusov 《Journal of Structural Chemistry》1994,35(1):101-114
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 相似文献
284.
285.
286.
Ll Abia X. L. Armesto M. Canle L. M. V. García M. Losada J. A. Santaballa 《国际化学动力学杂志》1994,26(10):1041-1053
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. 相似文献
287.
288.
An algorithm for finding a circumscribed triangle of the minimal perimeter is suggested. Properties of such a triangle are described. Bibliography: 1 title. 相似文献
289.
K. B. Aleinikova E. N. Zinchenko A. V. Arakcheeva V. V. Grinevich 《Crystallography Reports》2002,47(4):555-558
An amorphous sediment was prepared by the decomposition of potassium oxofluoroniobate K2 ? x Nb4O3(O, F)3F in water. For this sediment, the atomic radial distribution function was analyzed with the use of a fragment model, which allows one to interpret expanded coordination spheres as being formed by first several strongest diffusion maxima. These spheres carry the most reliable information on the structure. It is shown that the amorphous sediment consists of the randomly packed Nb(O,F)6-octahedra with interatomic distances close to those observed in the ordered region in the N-Nb2O5 structure. During decomposition in water, the initial K2 ? x Nb4O3(O, F)3F phase loses KF-layers, whereas Nb6 clusters with metal bonds are destroyed. 相似文献
290.