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21.
22.
Peter M. Tolstoy Sergei N. Smirnov Ilya G. Shenderovich Nikolai S. Golubev Gleb S. Denisov Hans-Heinrich Limbach 《Journal of Molecular Structure》2004,700(1-3):19-27
1H and 15N NMR spectra of 10 complexes exhibiting strong OHN hydrogen bonds formed by 15N-labeled collidine and different proton donors, partially deuterated in mobile proton sites, have been observed by low-temperature NMR spectroscopy using a low-freezing CDF3/CDF2Cl mixture as polar aprotic solvent. The following proton donors have been used: HCl, formic acid, acetic acid, various substituted benzoic acids and HBF4. The slow hydrogen bond exchange regime could be reached below 140 K, which allowed us to resolve 15N signal splittings due to H/D isotopic substitution. The valence bond order model is used to link the observed NMR parameters to hydrogen bond geometries. The results are compared to those obtained previously [Magn. Reson. Chem. 39 (2001) S18] for the same complexes in the organic solids. The increase of the dielectric constant from the organic solids to the solution (30 at 130 K) leads to a change of the hydrogen bond geometries along the geometric correlation line towards the zwitterionic structures, where the proton is partially transferred from oxygen to nitrogen. Whereas the changes of spectroscopic and, hence, geometric parameters are small for the systems which are already zwitterionic in the solid state, large changes are observed for molecular complexes which exhibit almost a full proton transfer from oxygen to nitrogen in the polar liquid solvent. 相似文献
23.
4-(3-Alkylureido)-2, 2, 6, 6-tetramethylpiperidine-1-oxyls are rapidly oxidized by N2O4 or NOCl to 4-(3-alkylureido)-2, 2, 6, 6-tetramethyl-1-oxopiperidinium nitrates and chlorides, which are then nitrosated to 4-(3-alkyl-3-nitrosoureido)-2, 2, 6, 6-tetramethyl-1-oxopiperidinium salts. The perchlorates of the latter were prepared by an exchange reaction with HClO4. The nitrosation of alkylureidooxoammonium salts is the first example of chemical modification of oxoammonium derivatives in which the highly reactive >N+=O group is inert toward the reagent.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 542–547, March, 1993. 相似文献
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The generation of matter in an extreme state with precisely measurable parameters is of great interest for contemporary physics. One way of obtaining such a state is to irradiate the end of a hollow cylindrical shell at the center of which a test material is kept at a temperature of several Kelvin by an annular beam of high-energy heavy ions. Under the action of the beam, the shell starts explosively expanding both outwards and inwards, compressing the material to an extremely high pressure without subjecting it to direct heating. A method of producing a hollow cylindrical beam of high-energy heavy ions using a resonance rf deflector is described. The deflection of the beam in two transverse directions by means of an rf electric field allows it to rotate about the longitudinal axis and irradiate an annular domain on the end face of the target. 相似文献
26.
D. V. Petkieva E. K. Golubev T. S. Kurkin A. S. Kechek’yan T. A. Rudakova M. A. Beshenko A. N. Ozerin 《Doklady Chemistry》2017,477(2):274-277
On the basis on polyvinyl alcohol (PVA), carbonized fibers were produced in the form of a complex technical thread with tensile strength above 200 MPa and specific electrical conductivity of at least 0.5 S/cm. Using thermogravimetric and differential thermal analysis, Raman scattering, and wide-angle X-ray diffraction, structures of these fibers were characterized. The structural parameters of carbonized PVA fibers are close to the parameters of carbonized coal tar pitch obtained by heat treatment at 1000°C. The structure and properties of carbonized fibers modified with potassium bisulfate were also studied. 相似文献
27.
The one-pot, three-step, four-component Ugi-IMDAF reaction with 5-hydroxymethylfurfural provides simple access to hydroxymethyl-substituted epoxyisoindolones in a diastereoselective and stereospecific manner. The protocol avoids the transfer or isolation of isocyanides, and the broad scope was illustrated by the synthesis of 22 different compounds bearing various substituents on the heterocyclic core. 相似文献
28.
E. R. Naranov V. O. Samoilov O. V. Golubev K. L. Zanaveskin A. L. Maksimov E. A. Karakhanov 《Russian Journal of Applied Chemistry》2018,91(10):1688-1693
Possibility of using mesoporous materials for obtaining Ni–Mo sorption-catalytic materials for purification of medium-distillate fractions to remove arsenic-containing compounds was examined. It was shown that, in the course of hydropurification, the acidity of the mesoporous material does not directly affect the extent to which the amount of arsenic in hydrocarbons is diminished. It was found that mesoporous supports of the SBA-15, TUD, and MCF types reduce the content of arsenic to less than 0.5 ppm at 360°C and 50 atm of H2. 相似文献
29.
One-electron oxidation of bis(4-tert-butylphenyl)aminoxyl with antimony pentachloride and bromine leads to the formation of oxoammonium salts with anions SbCl 6 ? and Br 3 ? respectively. The salt with the Br 3 ? anion converted at heating into a mixture of bromodiphenylamines which formed also from the aminoxyl as a result of previously unknown reaction of three-electron reductive bromination. The mechanisms of these reactions were assumed. 相似文献
30.
Four metal‐ion‐binding nucleosides, viz. 2,6‐bis(1‐methylhydrazinyl)‐9‐(β‐D ‐ribofuranosyl)‐9H‐purine ( 2a ) and its N‐acetylated derivative, 2b , 2,4‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐5‐(β‐D ‐ribofuranosyl)pyrimidine ( 3 ), and 2,4‐bis(1‐methylhydrazinyl)‐5‐(β‐D ‐ribofuranosyl)pyrimidine ( 4 ) have been synthesized. The ability of these nucleosides and the previously prepared 2,6‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐9‐(β‐D ‐ribofuranosyl)‐9H‐purine to form Pd2+‐ and Hg2+‐mediated complexes with uridine has been studied by 1H‐NMR spectroscopy. To obtain additional support for the interpretation of the NMR data, comparative measurements on the ternary‐complex formation between pyridine‐2,6‐dicarboxamide ( 5 ), pyrimidine nucleosides, and K2PdCl4 were carried out. 相似文献