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791.
N. P. Erchak V. Ya. Ryabova A. A. Kemme S. V. Belyakov 《Chemistry of Heterocyclic Compounds》1993,29(8):926-931
Successive alkylation of 3-pyridinecarboxaldehyde with allyl bromide and reaction of 1-allyl-3-formylpyridinium bromide with thiosemicarbazide gave 1-allyl-3-formylpyridinium bromide semicarbazone. X-ray diffraction analysis and quantum-chemical calculations with optimization of geometry were conducted on the semicarbazone synthesized. It was shown that quaternization of the nitrogen atom did not have any effect on the planarity of the heterocycle and the cationic charge was mainly localized on the thiosemicarbazone group, in which intramolecular hydrogen bonding is absent, despite the small interatomic separation of N...H-N.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1088–1093, August, 1993. 相似文献
792.
Halofluorination of norbornadiene with N-bromosuccinimide, N-chlorosuccinimide or xenon difluoride in the presence of polyhydrogen fluoride-pyridine resulted in the formation of three products: 3-endo-halo-5-exo-fluoro (2) and 3-exo-halo-5-exo-fluoronortricyclane (3), and 2-exo-fiuoro-7-syn-halo-norbornene-5 (4). The exo-attack of the electrophile on norbornadiene is slightly predominant (65% X = Br, 64% X = Cl, 73% X = F) over the endo-attack. The Meerwein-Wagner rearrangement occurred only in the case of chlorine or fluorine halosubstituents of β-carbonium ions formed by exo attack of the electrophile. 相似文献
793.
794.
795.
796.
Highly porous interpolymer ion-exchange membranes have been prepared from poly(styrene sulfonic acid), PSSA and poly(vinylidene fluoride) PVdF using a casting solvent of dimethylformamide and hexamethylphosphoramide. The membranes have been characterized by their water content, concentration potential, ionic conductivity, and their hydraulic permeability. An estimation of the porosity of the membranes has been made from the relative conductance of the potassium and the tetrabutylammonium ions in the film. This porosity has been compared with that derived from a consideration of the water flux through a Poiseuille-type pore. 相似文献
797.
A theory is developed for calculating the velocity of sound in solid-gas and liquid-gas systems. Using mass and momentum balances, an equation is obtained which shows that the velocity of sound depends on the relative velocity between the two phases, on the ratio of densities, on the porosity, on the particle diameter, on the drag coefficient, and on the frequency of sound.
The theory can be applied only if the one phase is distributed in the other homogeneously in the form of particles, droplets or bubbles of equal size. The experimental results agree very well with the theory.
Based on Hert'z equation for the deformation of spheres, a further theory is described which enables calculation of the velocity of sound in gas-solid systems of low porosity, such as packings or porous bodies. 相似文献
798.
799.
Teunissen Marcel J. de Kort Gregor V. M. Op Den Camp Huub J. M. Vogels Godfried D. 《Applied biochemistry and biotechnology》1993,39(1):177-189
Applied Biochemistry and Biotechnology - Three anaerobic fungi, twoNeocallimastix strains isolated from a ruminant (sheep) and onePiromyces strain isolated from a nonruminant (black rhinoceros),... 相似文献
800.