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排序方式: 共有217条查询结果,搜索用时 171 毫秒
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I. P. Trifonova V. A. Burmistrov A. S. Ocheretovyi O. I. Koifman 《Russian Journal of General Chemistry》2007,77(6):1078-1085
Inner-sphere replacement of alcohols by imidazole and its derivatives in the complex (acetato)-(tetraphenylporphyrinato)chromium(III) was studied by electronic absorption spectroscopy. The rate constants and activation parameters of the process were calculated. The entering ligand structure was shown to affect the reaction rate, while the alcohol nature (departing ligand) does not influence the kinetic parameters of the process to an appreciable extent. Regression analysis revealed participation of imidazole and ethanol in the rate-determining stages. The kinetic equation for the inner-sphere axial substitution implies interaction of a free alcohol molecule with that coordinated to chromium, followed by replacement of the associate by the heteroring. Mathematical processing of the kinetic data in terms of the proposed solvolytic association-dissociation mechanism gave the rate constants for particular stages of the process and showed an extremal relation between the rate constant and composition of the solvent. 相似文献
3.
Héctor Beltrán Nahum Masó Beatriz Julian Eloisa Cordoncillo Juan B. Carda Purificación Escribano Anthony R. West 《Journal of Sol-Gel Science and Technology》2003,26(1-3):1061-1065
Lead Magnesium Niobate, Pb(Mg1/3Nb2/3)O3 (PMN), is an important relaxor ferroelectric material. A significant problem exists, however, in the preparation of this material: it is very difficult to prepare pure phase, without the presence of a pyrochlore impurity phase which degrades the dielectric properties. Depending on the processing conditions, the amount of pyrochlore phase varies.Considering the ternary diagram PbO-MgO-Nb2O5, different compositions have been prepared by a simple sol-gel method at room temperature using Pb(CH3COO)2, Mg(CH3COO)2, Nb(OC2H5)5 as precursors. After the heat treatment, the samples obtained were analyzed by XRD and EPMA with the purpose of studying the compositions formed.From the analysis of these results, it seems to be that the appearance of pyrochlore can be related to the reactivity of the MgO and/or the presence of other phases of the binary system PbO-Nb2O5. An excess of Pb and Mg is necessary for compositions to be formed near the PMN. The control of the amount of these two elements is very important because an excess of MgO would lead to rich compositions in Mg as a secondary phase. 相似文献
4.
Genosar L Lasitza T Gepshtein R Leiderman P Koifman N Huppert D 《The journal of physical chemistry. A》2005,109(21):4852-4861
The pressure dependence of the excited-state proton dissociation rate constant of four photoacids, 2-naphthol-6,8-disulfonate (2N68DS), 10-hydroxycamptothecin (10-CPT), 5-cyano-2-naphthol (5CN2), and 5,8-dicyano-2-naphthol (DCN2), are studied in methanol. The results are compared with the results of the pressure dependence study we recently conducted for several photoacids in water, ethanol, and propanol. The pressure dependence is explained using an approximate stepwise two-coordinate proton transfer model. The increase in rate, as a function of pressure, manifests a strong dependence of proton tunneling on the distance which decreases with an increase of pressure between the two oxygen atoms involved in the process. The decrease in the proton transfer rate with increasing pressure reflects the dependence of the reaction on the solvent relaxation rate. We found that, for the relatively weak photoacids 2N68DS, 10-CPT, and 5CN2, the proton transfer rate constant increases by a factor of about 5-8 at a pressure of about 1.5 GPa. For a strong photoacid like DCN2, the rate increase was only by a factor of 2. 相似文献
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A. S. Semeikin O. I. Koifman B. D. Berezin 《Chemistry of Heterocyclic Compounds》1982,18(10):1046-1047
Condensation of p-nitrobenzaldehyde with pyrrole in propionic acid with added acetic anhydride gave tetrakis(4-nitrophenyl)porphin (24%), by the reduction of which tetrakis(4-aminophenyl)porphin, which was also obtained by hydrolysis of tetrakis(4-acetamidophenyl)porphin, was synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1354–1355, October, 1982. 相似文献
7.
O. V. Surov N. Zh. Mamardashvili G. P. Shaposhnikov O. I. Koifman 《Russian Journal of General Chemistry》2006,76(6):974-979
The temperature dependences of the vapor pressure of calix[4]arenes were determined by the Knudsen effusion method. Some calix[4]arenes can form congruently subliming intramolecular compounds with a solvent. The thermodynamic parameters of the sublimation of the compounds were calculated. Molecules of organic solvents incorporated in the cavity of calix[4]arenes stabilize the crystal lattice, increasing the enthalpy of sublimation. The electrostatic interactions presumably make a significant contribution to stabilization of the crystal lattice of stoichiometric complexes of calix[4]arenes with solvents. 相似文献
8.
Venediktov E. A. Rozhkova E. P. Koifman O. I. 《Russian Journal of Applied Chemistry》2012,85(3):477-478
Stable silver particles of 39 nm in diameter were synthesized by the thermal implantation of its ions in ED-20 epoxy oligomer. 相似文献
9.
Lebedeva N. Sh. Gubarev Yu. A. Zakharova G. V. Koifman O. I. 《Russian Journal of General Chemistry》2019,89(3):619-625
Types of dimers of aluminum and cobalt complexes of tetraanthraquinoneporphyrazines were identified. Thermodynamic characteristics of dissociation of the dimers in aqueous media were obtained. The kinetics of the deactivation of the triplet state of the aluminum complexes of sulfonated phthalocyanine and tetraanthraquinoneporphyrazine was studied.
相似文献10.
Bespalova G. N. Morokhina A. K. Shabunin E. K. Ageeva T. A. Koifman O. I. 《Russian Journal of General Chemistry》2021,91(3):528-533
Russian Journal of General Chemistry - A method was proposed for introducing cobalt resinate catalyst into VKF-093 primer-based waterborne compositions for electrodeposition. The colloidal-chemical... 相似文献