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371.
Alexandr Jegorov Ladislav Cvak Roman Bednář Jan Čejka Michal Hušák Bohumil Kratochvíl Ivana Císařová 《Structural chemistry》2006,17(1):131-137
Crystal forms of N-[3-(dimethylamino)propyl]-N-(ethylcarbamoyl)-6-allyl-ergoline-8β-carboxamide (cabergoline) originating from various solvents have been examined by X-ray diffraction at 298 or 150 K. Crystal structures of cabergoline anhydrate, (form II, P212121) and solvates (all P212121) with tert-butyl methyl ether (form VIII), cyclohexane (form XV), toluene (form IX), p-xylene (form XVI), and 1,2,4-trimethylbenzene (form XVII) are described. Conformation of cabergoline in these forms was compared with crystal structures of forms I and VII of cabergoline (P21) described in the literature. Despite a high degree of molecular conformational freedom, cabergoline possesses similar conformation in forms I, II, VIII, IX, XV, XVI, and XVII. Molecular conformations, crystal packing and the effect of the solvent on the former two properties are examined. 相似文献
372.
Free Radical Reactions of N-Heterocyclic Compounds, X[1]. – Radical Reactions of Cyclic 1,2-Diacylhydrazines Cyclic 1,2-diacylhydrazyls 3 have been detected by ESR spectroscopy during oxidation of the corresponding NH compounds 2 . The N coupling constants are determined and confirmed by simulation and by 15N labeling. The hydrazyls 3 react by dimerization to the corresponding tetrazanes of type 5 or by β scission to the diacyl azo compounds 4 and C radicals. The β scission of the radicals 3 is elucidated by UV/Vis detection of the azo compound 4b and reaction of 4b to Diels-Alder adducts. The alkyl radicals are trapped by nitrosobenzene ( 8 ) (ESR). 相似文献
373.
Ladislav Petruš Mária Petrušová Duy-Phong Pham-Huu Erika Lattová Božena Pribulová Jozef Turjan 《Monatshefte für Chemie / Chemical Monthly》2002,133(4):383-392
Summary. Since the development of the Sowden methodology in the middle of the twentieth century, several other efficient and complementary methods for the transformation
of sugar nitromethyl groups to aldehyde functionalities in their free, hemiacetal, or otherwise derivatized forms have been
developed. Hydrogen peroxide oxidation as well as ozonolysis of 1-deoxyalditol-1-nitronates in aqueous solution provide free
aldoses, thus presenting alternatives to the well-known Nef reaction. When applied to 2,5- or 2,6-anhydro-1-deoxy-1-nitroalditols, also known also as glycosylnitromethanes, the Nef reaction fails, and the hydrogen peroxide oxidation overoxidizes the expected products to 2,5- or 2,6-anhydroaldonic acids.
On the other hand, the ozonolysis of such compounds under pH-controlled conditions results in up to 85% of the interesting glycosylformaldehydes. The Nef reaction carried out in anhydrous low alcohols, however, has revealed a new conversion of glycosylnitromethanes to glycosylmethanal
dialkyl acetals, even more interesting C-glycoside synthons. A similar acid-catalyzed methanolysis of 1-deoxyalditol-1-nitronates
leads to methyl furanosides. Finally, a treatment of per-O-substituted glycosylnitromethanes with tributyltin hydride in boiling
benzene causes their radical reduction under a nearly quantitative formation of glycosylmethanal oximes.
Received November 12, 2001. Accepted November 20, 2001 相似文献
374.
Ladislav Pach Ján Majling Sridhar Komarneni 《Journal of Sol-Gel Science and Technology》2000,18(2):99-103
Monolithic boehmite gel discs (1.2 cm) of 0.12 and 0.25 mm thickness were examined by DTA, TGA, measurements of surface area, pore volume, pore radius and on-line measurements of optical transmittance from room temperature (RT) to 1200°C. The optical transmittance reflects the water liberation out of sample discs and provides information on processes associated with the phase/microstructure changes taking place such as the crystallization of the -alumina grains. 相似文献
375.
Stanislav Biskupič Ladislav Valko Vladimír Kvasnička 《Theoretical chemistry accounts》1975,38(2):149-157
A simple method of infinite summations of some dominant diagrams in the framework of the one-particle Green functions technique is suggested. This method for the calculation of the lowlying vertical ionization potentials of some simple closed-shell molecules described by CNDO/2 semiempirical Hamiltonian is applied. The obtained results are in quite-satisfactory agreement with the experimental values of the vertical ionization potentials measured by the photo-electron spectroscopy technique. 相似文献
376.
377.
The state of doping of fullerene peapods C60@SWCNT treated with K vapor was studied by in situ Raman spectroelectrochemistry. For all samples under study, a heavy chemical n doping was proved by the vanishing of the radial breathing mode and the downshift of tangential displacement mode. The K-treated peapods remain partly doped even if they are exposed to humid air. The Ag(2) mode of intratubular fullerene in K-doped peapods in contact with air was still redshifted as referred to its position in pristine peapods. Potassium inserted into the peapods is the reason for the air-insensitive residual doping, which can be removed only by electrochemical oxidation. This indicates the presence of two positions of potassium in doped sample. 相似文献
378.
Krause M Deutsch D Janda P Kavan L Dunsch L 《Physical chemistry chemical physics : PCCP》2005,7(17):3179-3184
Electrochemical reduction of ordered C60 fullerene films in aqueous solution was studied by AFM, FTIR and Raman spectroscopy, mass spectrometry and elastic recoil detection analysis. During the irreversible reduction process the film morphology changed from a heteroepitaxial (111) surface to a nanostructured array with clusters of 20 to 50 nm lateral size on average. On the molecular level the initial C60 underwent electrochemical reactions to form C60 polymers and hydrogenated C60. Chemical follow-up reactions of electrochemically formed C60- with water are responsible for the different reduction behaviour of C60 films in aqueous solution compared to C60 reduction in organic solvents and to C60 doping with alkali metals. Based on the spectroscopic analysis a reaction scheme accounting for the chemical processes at the C60 / aqueous electrolyte interface is presented. 相似文献
379.
Cyclizations of α,β‐unsaturated ketones with aminoguanidine under neutral conditions were examined. In contrast to literature reports of 1,2,4‐triazines as reaction products, formation of 5‐aryl‐4,5‐dihy‐dro‐3‐methyl‐1H‐pyrazole‐1‐carboximidamides and carboxamides was observed. An explanation based on the Hard‐Soft Acid‐Base principle is presented and the probable causes of divergent reaction pathways are discussed. 相似文献
380.
Ladislav Nebeský 《Czechoslovak Mathematical Journal》1998,48(4):701-710
We say that a binary operation * is associated with a (finite undirected) graph G (without loops and multiple edges) if * is defined on V(G) and uv E(G) if and only if u v, u * v = v and v * u = u for any u, v V(G). In the paper it is proved that a connected graph G is geodetic if and only if there exists a binary operation associated with G which fulfils a certain set of four axioms. (This characterization is obtained as an immediate consequence of a stronger result proved in the paper). 相似文献