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排序方式: 共有1122条查询结果,搜索用时 15 毫秒
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Bretonnière Y Mazzanti M Pécaut J Olmstead MM 《Journal of the American Chemical Society》2002,124(31):9012-9013
The simple asymmetric tetradentate ligand 2,2':6',2' '-terpyridine-6-carboxylic acid leads to the self-assembly of the first europium nanowheel containing europium ions in two different coordination environments. Moreover the self-assembly of bis(terpyridinecarboxylate) europium species to form a hexameric wheel capable of strongly binding LnIII cations is controlled by the ligand/cation ratio. 相似文献
4.
Giorgio Favini Demetrio Pitea Manuela Sottocornola Roberto Todeschini 《Journal of Molecular Structure》1982,87(1):53-64
The conformational geometries and possible interconversion paths for some oxa derivatives of bicyclo[5.1.0] octane have been studied by the molecular mechanics method. The theoretical results are compared with the experimental data for the molecular geometry of bicyclo[5.1.0] octane and 3,5,8-trioxabicyclo[5.1.0] octane, the free energy of activation for cycloheptene epoxide and 3,5-dioxabicyclo[5.1.0] octane, the dipole moments and molar Kerr constants in solution for cycloheptene epoxide, 3,5-dioxa- and 3,5,8-trioxabicyclo[5.1.0] octane. 相似文献
5.
Feth MP Bolm C Hildebrand JP Köhler M Beckmann O Bauer M Ramamonjisoa R Bertagnolli H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(6):1348-1359
XANES and EXAFS spectroscopic studies at the Mn-K- and Br-K-edge of reaction products of (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride ([(salen)Mn(III)Cl], 1) and (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) bromide ([(salen)Mn(III)Br], 2) with 4-phenylpyridine N-oxide (4-PPNO) and 3-chloroperoxybenzoic acid (MCPBA) are reported. The reaction of the Mn(III) complexes with two equivalents of 4-PPNO leads to a hexacoordinated compound, in which the manganese atom is octahedrally coordinated by four oxygen/nitrogen atoms of the salen ligand at an average distance of approximately 1.90 A and two additional, axially bonded oxygen atoms of the 4-PPNO at 2.25 A. The oxidation state of this complex was determined as approximately +IV by a comparative study of Mn(III) and Mn(V) reference compounds. The green intermediate obtained in reactions of MCPBA and solutions of 1 or 2 in acetonitrile was investigated with XANES, EXAFS, UV/Vis, and Raman spectroscopy, and an increase of the coordination number of the manganese atoms from 4 to 5 and the complete abstraction of the halide was observed. A formal oxidation state of IV was deduced from the relative position of the pre-edge 1s-->3d feature of the X-ray absorption spectrum of the complex. The broad UV/Vis band of this complex in acetonitrile with lambda(max)=648 nm was consistent with a radical cation structure, in which a MCPBA molecule was bound to the Mn(IV) central atom. An oxomanganese(V) or a dimeric manganese(IV) species was not detected. 相似文献
6.
[reaction: see text] A new mild method for protecting alcohols as t-butyl ethers is reported. The reaction proceeds with Mg(ClO4)2 and Boc2O and shows general applicability. The deprotection of t-butyl ethers has also been revisited. Preliminary results indicate the CeCl3 x 7H2O/NaI system is a very suitable catalyst for their removal. 相似文献
7.
The development and in-house testing of a method for the detection and quantification of cocoa butter equivalents in cocoa butter and plain chocolate is described. A database consisting of the triacylglycerol profile of 74 genuine cocoa butter and 75 cocoa butter equivalent samples obtained by high-resolution capillary gas liquid chromatography was created, using a certified cocoa butter reference material (IRMM-801) for calibration purposes. Based on these data, a large number of cocoa butter/cocoa butter equivalent mixtures were arithmetically simulated. By subjecting the data set to various statistical tools, reliable models for both detection (univariate regression model) and quantification (multivariate model) were elaborated. Validation data sets consisting of a large number of samples (n = 4050 for detection, n = 1050 for quantification) were used to test the models. Excluding pure illipé fat samples from the data set, the detection limit was determined between 1 and 3% foreign fat in cocoa butter. Recalculated for a chocolate with a fat content of 30%, these figures are equal to 0.3-0.9% cocoa butter equivalent. For quantification, the average error for prediction was estimated to be 1.1% cocoa butter equivalent in cocoa butter, without prior knowledge of the materials used in the blend corresponding to 0.3% in chocolate (fat content 30%). The advantage of the approach is that by using IRMM-801 for calibration, the established mathematical decision rules can be transferred to every testing laboratory. 相似文献
8.
Nilendu PandaNirup B Mondal Sukdeb BanerjeeNiranjan P Sahu Kazuo KoikeTamotsu Nikaido Manuela WeberPeter Luger 《Tetrahedron》2003,59(42):8399-8403
Three new polyhydroxy pregnanes named dregealol (1), volubilogenone (2) and volubilol (3) were isolated from the flowers of Dregea volubilis, and their structures elucidated from extensive 2D NMR analysis. The structure of volubilol (3) was confirmed by X-ray crystallographic studies. The known pregnane derivatives drevogenin D, iso-drevogenin P and 17α-marsdenin were also isolated. 相似文献
9.
Bonini BF Comes-Franchini M Mazzanti G Ricci A Sala M 《The Journal of organic chemistry》1996,61(21):7242-7243
10.
Alvisi D Blart E Bonini BF Mazzanti G Ricci A Zani P 《The Journal of organic chemistry》1996,61(20):7139-7146
The palladium-catalyzed desilylation-arylation of substituted vinylsilanes by p-iodoanisole in the presence of bidentate phosphine ligands is described. Apart from enhancing the rate of the reaction considerably, heteroatom-based functional groups in the vinylsilane moiety have a profound influence on the regiochemistry. A catalytic cycle for the chelation-controlled desilylation-arylation reaction involving five- and six-membered chelate rings is proposed. 相似文献