排序方式: 共有27条查询结果,搜索用时 10 毫秒
1.
Journal of Analytical Chemistry - Studies on the separation of the Se and Te trace components from Co, Ni, Cu, Fe, Cr, Mo, and W macrocomponents for their determination by inductively coupled... 相似文献
2.
We prove a uniform bound for the density, p
t
(x), of the solution at time t(0, 1] of a 1-dimensional stochastic differential equation, under hypoellipticity conditions. A similar bound is obtained for an expression involving the distributional derivative (with respect to x) of p
t
(x). These results are applied to extend the Itô formula to the composition of a function (satisfying slight regularity conditions) with a hypoelliptic diffusion process in the spirit of the work of Föllmer et al.
(5) 相似文献
3.
Nina I. Giricheva Georgiy V. Girichev Yulia S. Medvedeva Sergey N. Ivanov Anna V. Bardina Vyacheslav M. Petrov 《Structural chemistry》2011,22(2):373-383
A combined gas-phase electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pvtz, MP2/cc-pvtz) study of molecular
structure of 2-nitrobenzenesulfonamide (2-NBSA) was carried out. Quantum chemical calculations showed that 2-NBSA has four
conformers, two of which are stabilized by intramolecular hydrogen bond. The latter (with the S–N bond in a close to orthogonal
position around the phenyl ring and differing from each other by staggered or eclipsed positions of the N–H and S=O bonds
in the SO2NH2 group) presented in a saturated vapor over 2-NBSA at T = 433 (3) K in commensurable amounts. Experimental internuclear distances (Ǻ) for the staggered conformer are (?): r
h1(C–H)av. = 1.071(9), r
h1(C–C)av. = 1.390(4), r
h1(C–S) = 1.789(8), r
h1(S=O)av. = 1.427(6), r
h1(S–N) = 1.644(6), r
h1(N–O)av. = 1.221(4), r
h1(C′–N) = 1.487(8), r
h1(N–H)av. = 1.014. Calculations at B3LYP/cc-pvtz level were performed to determine the structure and the energies of the transition
states between conformers. It was shown that the conformer structures of free molecule differ from those of a molecule stabilized
by intermolecular hydrogen bonds in a crystal. Influence of a substituent X (X = –CH3, –NO2) on conformational features of the ortho-substituted benzenesulfonamide was established. 相似文献
4.
B. S. Tanaseichuk A. A. Bardina A. A. Khomenko 《Chemistry of Heterocyclic Compounds》1971,7(9):1180-1182
Dimers of 4(5)-phenyl-5(4)-β-naphthyl-2-phenyl-substituted imidazolyl radicals were synthesized in order to study the effect of a β-naphthyl group on the stability of triaryl-imidazolyl radicals, and the rate constants and energies of activation for dissociation of the dimers were determined. The presence of a β-naphthyl group in the bistriarylimid-azolyl molecule facilitates its dissociation into radicals as compared with bistriphenyl-imidazolyl. 相似文献
5.
E. N. Karaulova G. D. Gal'pern V. D. Nikitina T. A. Bardina L. M. Petrova 《Chemistry of Heterocyclic Compounds》1973,9(11):1337-1340
S-(4-Hydroxyaryl)sulfoniacyclane perchlorates have been obtained by the condensation of thiacyclanes with phenols in the presence of perchloric acid, phosphorus oxychloride, and hydrogen peroxide, or by condensing thiacyclane S-oxides under the same conditions but without the hydrogen peroxide. The capacity for forming sulfonium perchlorates decreases sharply in the sequence tetrahydrothiophene >thiacyclohexane>thiacycloheptane > methylthiacyclohexane; no sulfonium salts are obtained under these conditions from 2,2,6,6-tetramethylthiacyclohexane, 2-methyl-1-thiadecalin, or 2,5-dimethyltetrahydrothiophene. The S-(4-hydroxyaryl)sulfoniacyclane perchlorates take part in double-decomposition reactions, giving picrates, chlorides, and phosphates. The action of caustic potash in methanol on S-(4-hydroxyphenyl)tetrahydrothiophenium salt forms a dimeric sulfobetaine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1479–1482, November, 1973. 相似文献
6.
V. N. Shishkin B. S. Tanaseichuk L. G. Tikhonova A. A. Bardina 《Chemistry of Heterocyclic Compounds》1973,9(3):358-361
Ten series of triarylimidazoles were subjected to polarographic oxidation. It was found that electron-donor substituents facilitate polarographic oxidation, while electron-acceptor substituents hinder it. Correlation equations in coordinates of E1/2 and
+ were found for all of the investigated series.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 387–390, March, 1973.The synthesis and characteristics of the investigated imidazoles were described in [7–10]. 相似文献
7.
Petrov VM Girichev GV Oberhammer H Petrova VN Giricheva NI Bardina AV Ivanov SN 《The journal of physical chemistry. A》2008,112(13):2969-2976
The molecular structure and conformational properties of para-methylbenzene sulfonamide (4-MBSA) and ortho-methylbenzene sulfonamide (2-MBSA) have been studied by gas electron diffraction (GED) and quantum chemical methods (B3LYP/6-311+G** and MP2/6-31G**). Quantum chemical calculations predict the existence of two conformers for 4-MBSA with the S-N bond perpendicular to the benzene plane and the NH2 group either eclipsing or staggering the S-O bonds of the SO2 group. Both conformers possess CS symmetry. The eclipsed form is predicted to be favored by DeltaE = 0.63 kcal/mol (B3LYP) or 1.00 kcal/mol (MP2). According to the calculations, the S-N bond in 2-MBSA can possess planar direction opposite the methyl group (phi(C2C1SN) = 180 degrees ) or nonplanar direction (phi(C2C1SN) approximately 60 degrees ). In both cases, the NH2 group can adopt eclipsed or staggered orientation, resulting in a total of four stable conformers. The nonplanar eclipsed conformer (C1 symmetry) and the planar eclipsed form (CS symmetry) are predicted to be favored. According to the GED analysis, the saturated vapor over solid 4-MBSA at T = 151(3) degrees C consists as mixture of the eclipsed (78(19) %) and staggered (22(19) %) forms. The saturated vapor over solid 2-MBSA at T = 157(3) degrees C consists as a mixture of the nonplanar eclipsed (69(11) %) and planar eclipsed (31(11) %) forms. 相似文献
8.
V. M. Petrov N. I. Giricheva G. V. Girichev V. N. Petrova S. N. Ivanov A. V. Bardina 《Journal of Structural Chemistry》2011,52(1):60-68
A combined gas electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pVTZ) study of the molecular structure of 2-nitrobenzenesulfonic acid (2-NBSA) is performed. Quantum chemical calculations show that the 2-NBSA molecule has five conformers, and the Gibbs energy of one of them is lower by more than 4.5 kcal/mol than the energy of the other conformers. It is found experimentally that the saturated vapor of 2-NBSA at T = 394(5) K contains only the low-energy conformer that has an intramolecular hydrogen bond between the H atom of the hydroxyl group and one of the O atoms of the NO2 group. The C-C-S-O(H) torsion angle determining the position of the S-O(H) bond is ?72(7)°, while the NO2 group is substantially turned relative to the benzene ring plane (C1-C2-N-O = 40(5)°). The following experimental values of the internuclear distances are obtained for this conformer (Å): r h1(C-H)av = 1.07(2), r h1(C-C)av = 1.401(4), r h1(C-S) = 1.767(6), r h1(S=O)av = 1.412(4), r h1(S-O) = 1.560(6), r h1(N-O)av = 1.217(5), r h1(C-N) = 1.461(8), r h1(O-H) = 0.99(3). 相似文献
9.
T. A. Bazhenova N. V. Bardina G. N. Petrova M. A. Borovinskaya 《Russian Chemical Bulletin》2004,53(8):1646-1654
The effect of potential value and chemical properties of an external electron donor on C2H2 reduction catalyzed by nitrogenase active center (cluster [(6-N)Fe7MoS9·homocitrate] FeMoco isolated from the enzyme) has been investigated in the presence of proton donors of different acidity. The temperature—reaction rate dependences of these reactions have been studied. It has been shown that the rate-limiting steps of the reactions differ depending on the proton donor used. When thiophenol or water are used as proton donors, and electrochemical step — the electron transfer from cathode to adsorbed catalytic cluster — has been found to be a rate-limiting one. The effective activation energy of ethane formation as a product of four-electron C2H2 reduction is found to be 1.5 times lower than that of ethylene, namely, 13 kcal mol–1. When stronger acid, pentafluorothiophenol, is used as a proton donor, the chemical step of intramolecular rearrangement of the catalyst—substrate complex taking place in solution becomes a rate-limiting one. The effective activation energies of both ethylene and ethane become equal to 32 kcal mol–1.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1583–1591, August, 2004. 相似文献
10.
Reaction of vanadium pentafluoride with trichloroethene, tetrabromoethene, hexachlorobenzene, and octachloronaphthalene at −20 to 50 °C gave products from fluorine addition, CFCl2CFClH, C2Br4F2, C6Cl6F6, and C10Cl8F8, respectively. The fluorine addition to pentachloropyridine and hexabromobenzene was accompanied by the partial replacement of halogen atoms by fluorine and led to products C5Cl4F5N and C6Br4F8, respectively. 相似文献