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排序方式: 共有1306条查询结果,搜索用时 31 毫秒
21.
Nikolay TzvetkovMarc Schmidtmann Achim MüllerJochen Mattay 《Tetrahedron letters》2003,44(32):5979-5982
Bicyclo[3.3.0]octanone and bicyclo[4.3.0]nonanone derivatives with a cyclopropane unit in the α-position and an unsaturated side chain in the γ-position of the carbonyl group undergo fragmentation-cyclization processes leading to quasi-triquinane systems upon reductive photoinduced electron transfer (PET). For example, the new angular triquinane derivative 6 and the new propellane derivative 12 were synthesized in one step from these starting materials in moderate to good yields. 相似文献
22.
Sergei D. Kirik Julia N. Zaitseva Igor S. Yakimov Nikolay N. Golovnev 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):i159-i160
Lithium sodium aluminium fluoride was obtained as a white powder by melting a stoichiometric mixture of AlF3, NaF and LiF at 1223 K, and then cooling to 923 K and sintering at this temperature for 4 h. The ab initio crystal structure determination was carried out using X‐ray powder diffraction techniques. The monoclinic structure of LiNa2AlF6 can be related to cubic elpasolite. The Li and Al atoms lie on inversion centres. The main octahedral AlF6 structural elements are not deformed, but are rotated slightly with respect to the unit‐cell axes. The Li atoms have octahedral coordinations, whereas the Na atoms have cubo‐octahedral coordinations. The Na coordination polyhedron is distorted in comparison with that of elpasolite. 相似文献
23.
Roman L. Antipin Elena K. Beloglazkina Nikolay V. Zyk Nikolay S. Zefirov 《Tetrahedron letters》2007,48(4):729-731
Arylselenenation of conjugated and non-conjugated dienes by arylselenenamides in the presence of phosphorus(V) oxyhalides has been studied. Reactions with conjugated dienes lead to 1,4-adducts whilst only addition to double bonds takes place in reactions with non-conjugated dienes. 相似文献
24.
Z. Popova C. Dimitrov K. Aristirova R. P. Dimitrova L. Dukova G. Wendt 《Reaction Kinetics and Catalysis Letters》1988,36(1):85-90
Two series of nickel mordenite catalysts have been prepared on the basis of Na-mordenite and H-mordenite. Their catalytic activity in cyclohexane conversion has been studied. It has been found that the properties of the catalysts are strongly dependent on the acidity of mordenite.
NaM HM. .相似文献
25.
A new procedure for the preparation of high aspect ratio Au nanowires utilizing gold electroless reduction in the hexagonally ordered, thiol-modified nanosized channels of the SBA-15 material is reported. Two different Au precursors were adsorbed onto pedant thiol groups, covalently bonded to the mesoporous silica surface, and used as seeds to grow extended Au nanostructures by treatment in Au electroless reduction bath. It is shown that the dimensions and the assembly of the Au seeds are important parameters for the subsequent electroless reduction process. The [AuCl4]- ions complexed to the TOAB molecules assembled on the thiol-modified mesoporous surface of the SBA-15 material are suitable precursors for the subsequent gold electroless reduction. The resulting structures are several micrometer long Au nanowires with uniform diameters of about 5 nm, having large single-crystalline domains. The TEM results clearly show that the growth of the Au nanowires is templated by the channel structure of the SBA-15 material. 相似文献
26.
Yulu Yang Mingguang Wu Xingwang Zhu Hui Xu Si Ma Yongfeng Zhi Hong Xia Xiaoming Liu Jun Pan Jie-Yinn Tang Siang-Piao Chai Leonardo Palmisano Francesco Parrino Junli Liu Jianzhong Ma Ze-Lin Wang Ling Tan Yu-Fei Zhao Yu-Fei Song Pardeep Singh Pankaj Raizada Deli Jiang Di Li R. A. Geioushy Jizhen Ma Jintao Zhang Song Hu Rongjuan Feng Gang Liu Minghua Liu Zhenhua Li Mingfei Shao Neng Li Jiahe Peng Wee-Jun Ong Nikolay Kornienko Zhenyu Xing Xiujun Fan Jianmin Ma 《中国化学快报》1990,30(12):2065-2088
This roadmap demonstrates a series of two-dimensional nanomaterials, such as graphene, black phosphorus, oxides, layered double hydroxides, chalcogenides, bismuth-based layered compounds, MXenes, metal organic frameworks, covalent organic frameworks, and others, for environmental catalysis. 相似文献
27.
Nikolay Tyutyulkov Ivo Kanev Oskar Polansky Jürgen Fabian 《Theoretical chemistry accounts》1977,46(3):191-203
The analysis of experimental data for singlet transitions (E
n) of even polyenes (I), cations (II) and anions (III) of odd polyenes show that for infinite chains E
(I)/E
(II)=E
(I)/E
(III) = 2:1. It is shown that the energy gap is equal for the three systems. In cases (II) and (III) there is a level (NBMO) in the gap which is vacant in (II) and occupied in (III). That is why the first optical transition in (II) and (III) depends on the semiwidth of the gap. 相似文献
28.
Janko Dimitriev Michail Arnaudov Vesselin Dimitrov 《Monatshefte für Chemie / Chemical Monthly》1976,29(21):1335-1343
Studies of glasses and their crystalline products in the TeO2–V2O5 system were made in the 1400–400 cm–1 range. A continuous shift of the V=O-band from 1020 cm–1 to 940 cm–1 was found in the glasses with decreasing concentration of V2O5, as well as a sharp decrease in the intensity at 830 cm–1. On the basis of the results obtained, it is concluded that with increasing TeO2 content, the structure of the glasses is changed, caused by the breaking of the V–O–V bonds and the formation of Te–O–Te bridges.The IR-spectrum of the 2TeO2·V2O5 compound in both crystalline and vitreous states was studied for the first time. The behaviour of the absorption bands is related to the structure of the glasses studied. 相似文献
29.
A simple oxide classification has been proposed on the basis of correlation between electronic polarizabilities of the ions and their binding energies determined by XPS. Three groups of oxides have been considered taking into account the values obtained on refractive-index- or energy-gap-based oxide ion polarizability, cation polarizability, optical basicity, O 1s binding energy, metal (or nonmetal) binding energy, and Yamashita-Kurosawa's interaction parameter of the oxides. The group of semicovalent predominantly acidic oxides includes BeO, B2O3, P2O5, SiO2, Al2O3, GeO2, and Ga2O3 with low oxide ion polarizability, high O 1s binding energy, low cation polarizability, high metal (or nonmetal) outermost binding energy, comparatively low optical basicity, and strong interionic interaction, leading to the formation of strong covalent bonds. Some main group oxides so-called ionic or basic such as CaO, In2O3, SnO2, and TeO2 and most transition metal oxides show relatively high oxide ion polarizability, O 1s binding energy in a very narrow medium range, high cation polarizability, and low metal (or nonmetal) binding energy. Their optical basicity varies in a narrow range and it is close to that of CaO. The group of very ionic or very basic oxides includes CdO, SrO, and BaO as well as PbO, Sb2O3, and Bi2O3, which possess very high oxide ion polarizability, low O 1s binding energy, very high cation polarizability, and very low metal (or nonmetal) binding energy. Their optical basicity is higher than that of CaO and the interionic interaction is very weak, giving rise to the formation of very ionic chemical bonds. 相似文献
30.
Maria Atanassova Victoria Lachkova Nikolay Vassilev Sabi Varbanov Ivan Dukov 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):173-179
The synergistic solvent extraction of five selected lanthanoid ions (La3+, Nd3+, Eu3+, Ho3+ and Lu3+) with a 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone(HP) and the 5,11,17,23-tert-butyl-25,26,27,28-tetrakis(dimethylphosphinoylmethoxy)calix[4]arene, (S) in CHCl3 has been studied. It was found that in presence of this phosphorus-containing calix[4]arene the lanthanoids have been extracted
as LnP3 · S. On the basis of the experimental data, the values of the equilibrium constants have been calculated. The influence of
the synergistic agent on the extraction process has been discussed. A synergistic effect of almost three orders of magnitude
occurs in the extraction of Ln(III) with mixture of HP and S. The values of the separation factors (S.F.) between the adjacent
elements have been evaluated.
On the basis of the IR and NMR spectra the stoichiometry and the structure of the solid complexes of Eu(III) with HP and Eu(III)
with HP and S were proposed. 相似文献