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排序方式: 共有268条查询结果,搜索用时 15 毫秒
261.
Masoumeh Vafaei-Nezhad Ghiasi Reza Shafiei Fatemeh 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2020,94(4):772-777
Russian Journal of Physical Chemistry A - This research aimed at exploring the stabilities of the conformers of 2-methoxy-2-oxo-1,3,2-dioxaphosphorinane and its methylthio and methylselenyl analogs... 相似文献
262.
We report the results of density functional theory (DFT) calculations of ethylene adsorption over the most stable pure and bimetallic clusters of Fe(n)Cu(m) (2 ≤ m+n ≤ 4), in two adsorption modes of π and di-σ. Our results show that the quality of interaction of ethylene with iron center in bimetallic clusters of iron-copper is characteristically different from what is found over pure iron. Over the range of our studies for dimers, trimers, and tetramers, whether for π or di-σ mode, alloying iron clusters results in a substantial improvement in adsorption of ethylene over cluster and exhibits a notable increase in binding and interaction energies compared with pure iron clusters. One of the interesting features of this adsorption is that ethylene never orients toward di-σ mode for Cu-Cu or Fe-Cu bonds, and π orientation is strongly preferred. Ethylene adsorption in di-σ coordination is accompanied by the sever restructuring, larger deformation energy, and the larger interaction energy. In the next part, we answer this question of how electronic perturbations induced by copper atoms can enhance the activity of iron toward ethylene. This interpretation is done within the framework of natural bond orbital (NBO) and natural resonance theory (NRT) analyses. Different reaction pathways detected by NRT analysis (donor-acceptor, metallacyclic, and carbanion) reveal interesting aspects of differences between the nature of metal-alkene coordination in bimetallic and purely metallic clusters. 相似文献
263.
264.
Majid M. Heravi Masoumeh Zakeri Narges Karimi Mina Saeedi Hossien A. Oskooie Niloofar Tavakoli-Hosieni 《合成通讯》2013,43(13):1998-2006
2,4,5-Trisubstituted imidazoles have been synthesized in excellent yields (85–95%) in the presence of 5 mol% of [(CH2)4SO3HMIM][HSO4] as a Brønsted acidic ionic liquid. 相似文献
265.
Mohammad?Mehdi?Kashani-MotlaghEmail author Masoumeh?Karami?Mahmoudabad 《Journal of Sol-Gel Science and Technology》2011,59(1):106-110
Our goal in this research was to obtain lead oxide nano-powders by sol–gel method. In this method, lead oxide nano-powders
were synthesized through the reaction of citric acid (C6H7O8·H2O) solution and lead acetate [Pb(C2H3O2)2] solution as stabilizer and precursor, respectively. The effect of different parameters including calcination temperature,
(molar ratio of citric acid to lead acetate) and drying conditions were investigated. The prepared lead oxide nano-powders
were characterized by FT-IR spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy.
The prepared PbO samples consist of the particles in the range of 50–120 nm or the thick plate like structures with thickness
of 53 nm depending on the drying conditions. 相似文献
266.
Abbas Afkhami Tayyebeh Madrakian Reza Ahmadi Hasan Bagheri Masoumeh Tabatabaee 《Mikrochimica acta》2011,175(1-2):69-77
We have developed a solid phase extraction method for the determination of cadmium ions in aqueous samples. It is based on the adsorption of Cd(II) on alumina nanoparticles coated with sodium dodecyl sulfate and modified with a newly synthesized Schiff base. Analytical parameters such as pH value, amount of adsorbent, type and concentration of eluent, flow rates of the sample and eluent, sample volume and matrix effects were optimized. Desorption is accomplished with 2?mol?L?1 nitric acid. Cd(II) was then determined by flame atomic absorption spectrometry. The maximum enrichment factor is 75. Under the optimum experimental conditions, the detection limit is 0.14???g?L?1 in original solution. The adsorption capacity of the modified sorbent is 4.90?mg?g?1 for cadmium ions. The method was applied to the determination of trace quantities of Cd(II) in water, wastewater, and biological and food samples with satisfactory results. Figure
Schematic representation of the loading L on the alumina nanoparticles 相似文献
267.
Mohammad T. Baei Parviz Torabi Ali Varasteh Moradi Masoumeh Moghimi 《Monatshefte für Chemie / Chemical Monthly》2011,18(3):783-788
Abstract
Nuclear magnetic resonance (NMR) parameters including isotropic and anisotropic chemical shielding parameters and electronic structures were calculated using density functional theory (DFT) for silicon–carbide-doped boron phosphide nanotubes. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using the Gaussian 03 program suite. The isotropic and anisotropic chemical shielding parameters were calculated for the sites of various 13C, 29Si, 11B, and also 31P atoms in pristine and SiC-doped (6,0) zigzag boron phosphide nanotube models. The calculations indicated that doping of 11B and 31P atoms by C and Si atoms had a more significant influence on the calculated shielding tensors than did doping of the B and P atoms by Si and C atoms. In comparison with the pristine model, Si- and C-doping of P and B sites of the zigzag nanotubes reduces the energy gaps of the nanotubes and increases their electrical conductance. 相似文献268.
V(HSO_4)_3 has been found to be an efficient reagent for the promotion of the oxidation of alcohols and trimethylsilyl, tetrahydropyranyl and methoxymethyl ethers to their corresponding carbonyl compounds with Cu(NO_3)_2·3H_2O in the absence of solvent. 相似文献