排序方式: 共有127条查询结果,搜索用时 0 毫秒
71.
72.
Volodymyr Semeniuchenko Yana Garazd Myroslav Garazd Tetyana Shokol Ulrich Groth Volodymyr Khilya 《Monatshefte für Chemie / Chemical Monthly》2009,25(3):1503-1512
Abstract
A highly efficient procedure for glucosylation of flavonoids by acetobromoglucose is described. Glucosylation is carried out in a two-phase system CHCl3/H2O over 96 h using tetrabutylammonium bromide as phase-transfer catalyst. A purification procedure can be performed without column chromatography, and the yields of the glucosylated flavonoids are mostly quantitative. Acetylated glucosides were deprotected with sodium methanolate to afford the desired glucosides of flavonoids. 相似文献73.
In present work, an effective method to research geometrically nonlinear free vibrations of elements of thin-walled constructions that can be modeled as laminated shallow shells with complex planform is applied. The proposed method is numerical–analytical. It is based on joint use of the R-functions theory, variational methods, Bubnov–Galerkin procedure and Runge–Kutta method. The mathematical formulation of the problem is performed in a framework of the refined first-order shallow shells theory. To implement the developed method, appropriate software was developed. New problems of linear and nonlinear vibrations of laminated shallow shells with clamped cutouts are solved. To confirm reliability of the obtained results, their comparison with the ones known in the literature is provided. Effect of boundary conditions is studied. 相似文献
74.
Dmytro M. Khomenko Tetyana V. Shokol Roman O. Doroshchuk Viktoriia S. Starova Ilona V. Raspertova Sergiu Shova Rostyslav D. Lampeka Yulian M. Volovenko 《Journal of heterocyclic chemistry》2021,58(6):1278-1285
New representatives of [1,2,4]triazolo[1,5-a]pyridine-8-carbonitriles were synthesized via the condensation of β-diketones or β-dialdehydes and characterized using MS spectrometry, 1H, 13C and, 19F NMR and IR spectroscopy. Crystal structures of two compounds were established using X-ray analysis and showed that title compounds are prone to the formation of planar molecules. The absence of band responsible for CN stretching vibration in trifluoromethyl-containing compounds was explained using the DFT calculations method, which also showed a significant influence of fluorines introducing on the energy gap between HOMO and LUMO. 相似文献
75.
Vyacheslav S. Grinev Oksana A. Mayorova Tatyana V. Aniskova Alexandra S. Tikhomolova Alevtina Yu. Yegorova 《Molecules (Basel, Switzerland)》2021,26(8)
3-(2-Chlorobenzylidene)-5-(p-tolyl)furan-2(3H)-one (1), C18H13ClO2, crystallizes with Z = 8 and Z′ = 2, and the structure at 100 K has orthorhombic (Pna21) symmetry. Each kind of molecule takes part in π–π stacking interactions to form infinite chains parallel to the c axis. We believe that the existence of two forms can be explained by the probable rotation around a single C–C bond. The quantum chemical modeling reveals that these molecules are almost equivalent energetically, and they can be described as the two most stable conformers (rotamers) with a minor rotational barrier of about 0.67 kcal/mol. 相似文献
76.
Irina Lebedyeva Tetyana Zheltonozhskaya Valeriy Yashchuk Vladislav Kudrya Ol'ga Demchenko 《Macromolecular Symposia》2001,166(1):243-248
The peculiarities of sorbtion mechanism of phenole molecules by poly(vinylalcohol) and poly(acrylamide) (PVA‐PAAN) films are examined. An analytical model of absorbtion process based on diffusive character of penetration of phenole molecules in polymer film with the following spontaneous capturing by selftuning traps is proposed. The analytical results can be easy compared with experimental data obtained by spectrophotometry method. The comparison of theory and experiment gives the average value of resulting diffusion lenght of phenole molecule during «free» life‐time <l>∼10−6 cm. 相似文献
77.
Sergiy O. Nikitin Rostyslav D. Lampeka Yulian M. Volovenko Tetyana A. Volovnenko Viktoria V. Dyakonenko Svitlana V. Shishkina Oleg V. Shishkin 《Polyhedron》2008
A series of new 3d-metal complexes based on 2-amino-3-(1-methylbenzimidazol-2-yl)-4(5H)-ketothiophen (HL1) and 2-amino-3-(2-benzothiazolyl)-4(5H)-ketothiophen (HL2) were synthesized. Compounds of the general formulas [ML2] and [M(HL1)2Cl2] (where M = Co2+, Ni2+, Zn2+, Cu2+) were prepared by the reaction of the above mentioned ligands with the corresponding acetate (for [ML2]) or chloride (for [M(HL1)2Cl2]) salts in a methanol or a methanol–chloroform medium. The choice of the anion in the initial metal salt, as well as the selection of the ligand, is crucial for obtaining coordination compounds with a neutral or deprotonated form of the 2-amino-4(5H)-ketothiophens. Thus, in contrast to HL1, complexes with the neutral form of HL2 cannot be obtained under the same conditions. All the complexes were studied by spectroscopic methods and X-ray crystallography (for [CuL12] · H2O). The coordination polyhedron of the copper atom is formed by four nitrogen atoms from two ligand anions and the geometry of the coordination sphere is intermediate between tetrahedral and square-planar. 相似文献
78.
79.
Mieczysław T. Borowiec Tetyana Zayarnyuk Maria U. Gutowska Jarosław Więckowski Andrzej Szewczyk Vladimir Dyakonov Eduard Zubov Marek Barański Viktor Domukhovski Maria C. Pujol Magdalena Aguiló Francesc Díaz Henryk Szymczak 《Central European Journal of Physics》2013,11(3):394-396
Investigations of the specific heat of the potassium gadolinium double tungstate KGd(WO4)2 have been performed over the temperature range from 0.05 K up to 4 K in zero magnetic field. The λ -type anomaly observed at T = 0.42 K was interpreted as an indication of a second order magnetic phase transition within the Gadolinium sublattice. The critical exponent α was determined from experimental data. 相似文献
80.
Shafran Y Rozin Y Beryozkina T Zhidovinov S Eltsov O Subbotina J Leban J Novikova R Bakulev V 《Organic & biomolecular chemistry》2012,10(30):5795-5798
Novel self-condensation of 3-(azol-5-yl)-1,1-dimethylenamines has been found to form new C-C bonds leading to 2,4-(1,2,3-triazole-1,2,3-thiadiazole-3-phenylisothiazole)-(1E,3Z)-5-yl-butadiene-1-amines. The discovered reaction represents a new example of C-H functionalization in unsaturated systems and can serve an efficient synthetic approach to rational design of new 2,4-(diazole-5-yl)-dieneamines. 相似文献