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排序方式: 共有181条查询结果,搜索用时 31 毫秒
31.
Bondarenko L Hentschel S Greiving H Grunenberg J Hopf H Dix I Jones PG Ernst L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(14):3950-3963
A selection of pseudo-geminally substituted [2.2]paracyclophanes, the alkynes 6, 7, 10, 11 a, and 11 b and the alkenes 8 and 9 were prepared for the study of intraannular reactions between functional groups in direct juxtaposition. Whereas 9 and 10 provide the corresponding cyclobutane and cyclobutene derivatives on irradiation (12 and 13, respectively), the bis-alkynes 7 and 11 b do not lead to a cyclobutadiene intermediate. In the latter case the "half-closed" butadiene derivative 17 was isolated. A Paterno-Büchi reaction took place on irradiation of 8 and 6, although the oxetene intermediate 21 produced in the second example did not survive the reaction conditions (ring-opening to 22). Bromine addition to 9, 10, and 7 occurred with high stereoselectivity (formation of the dibromides 27, 30, and 33, respectively), and is rationalized by postulating the formation of the cationic intermediates 26, 29, and 32, respectively. To study the interaction of a carbocation with a facing triple bond, the alcohol 34 was prepared from 6. On acid treatment ring closure to the triply-bridged phane 38 took place, accompanied by the hydration of the triple bond to the ketoalcohol 37. In an interesting intraannular [2+3]cycloaddition reaction the bis-acetylene 11 a, on treatment with n-butyl lithium, provided the cyclopentadiene derivative 42. That the two triple bonds of a pseudo-geminal diacetylene can engage in a cyclization reaction leading to the cyclopentadienone complex 44 was also shown by treating 11 b with iron pentacarbonyl. 相似文献
32.
van Bommel MR Berghe IV Wallert AM Boitelle R Wouters J 《Journal of chromatography. A》2007,1157(1-2):260-272
Chromatographic and spectroscopic techniques are evaluated for the analysis of early synthetic dyes. The research focuses on the analysis of dyestuffs that were developed and used in the period 1850-1900, which has not been well investigated so far. The aim of this study was to develop and evaluate techniques that can be applied in the field of culture and art. A selection of 65 synthetic dyestuffs was chosen to investigate the usefulness of the analytical techniques applied. As a case study three embroideries, designed by the well-known 19th century French painter Emile Bernard, were investigated to obtain more information about the use and behaviour of synthetic dyes. 相似文献
33.
Hydrogenselenates of Rare Earth Elements: Syntheses and Crystal Structures of La(HSeO4)3 and Gd(HSeO4)(SeO4) Colorless transparent single crystals of La(HSeO4)3 (hexagonal, P63/m, Z = 2, a = 971.7(1), c = 616.98(8) pm, Rall = 0.0440) were obtained from the reaction of La2O3 and conc. selenic acid. La(HSeO4)3 is isotypic with the corresponding hydrogensulfate. Its structure can be seen as a variant of the UCl3 type structure with complex anions and contains the La3+ ions in ninefold coordination of oxygen atoms. Single crystals of Gd(HSeO4)(SeO4) crystallize from a solution of Gd2O3 in selenic acid (70% H2SeO4). In the orthorhombic crystal structure (Pbca, Z = 8, a = 920.4(1), b = 1351.6(2), c = 1004.0(1) pm, Rall = 0.0276) the Gd3+ ions are coordinated by eight oxygen atoms belonging to four SeO42– and four HSeO4– ions. These are surrounded by four Gd3+ ions. 相似文献
34.
35.
Multianalytical Study of Patina Formed on Archaeological Metal Objects from Bliesbruck-Reinheim 总被引:1,自引:0,他引:1
Michael Wadsak Ina Constantinides Guido Vittiglio Annemie Adriaens Koen Janssens Manfred Schreiner Freddy C. Adams Philippe Brunella Michel Wuttmann 《Mikrochimica acta》2000,133(1-4):159-164
Patinas naturally formed on archaeological bronze alloys were characterized using light microscopy (LM), micro energy dispersive
X-ray fluorescence analysis (μ-EDXRF), time of flight secondary ion mass spectrometry (TOF-SIMS) and scanning electron microscopy
in combination with energy dispersive X-ray microanalysis (SEM/EDX). The examinations carried out on cross-sections of samples
have shown that in all samples the copper content in the corrosion layer is lower than in the bulk, while an increase of tin
and lead could be observed. Two different types of corrosion were found: first type, a corrosion formation leading to a three
layer structure was observed on lead bronze. The outer layer consists mainly of Cu(II) compounds and soil material, followed
by a fragmented layer of cuprous oxide and the surface layer of the alloy, where a depletion of copper and an enrichment of
tin and high amounts of Cl could be detected. The second type of corrosion is characterized by a two layer structure on the
tin bronze sample consisting of an outer layer with copper containing corrosion products and a layer with cracks, which reveals
a depletion of copper whereas tin and lead are enriched. Also high amounts of Si were detected in this surface layer. 相似文献
36.
37.
During stress-induced transformation NiTi shows a distinct generation of transformation bands. A simple one-dimensional model for superelastic NiTi wires has been developed to show exemplarily methods to account for these bands in plasticitybased models. To clarify the dependence of the transformation bands on the distribution of latent heat and therefore on the mechanical behaviour, optical and thermographical experiments have been performed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
38.
Jonas König Ina Dartsch Eric Sperlich Eva Guillamón Rosa Llusar Martin Köckerling 《无机化学与普通化学杂志》2020,646(18):1531-1538
Octahedral clusters of the [M6X12] type offer numerous possibilities to form structural arrangements through different choices of bonding situations. In this paper a series of new cluster compounds of the transition metal niobium is described, which consist of the [Nb6Cl18]2–, and in one case [Nb6Cl18]3–, anion and protonated N-base cations ([MIm-H]+, [nPr3N-H]+, [TMGu-H]+, and [Tzn-H]+). They all are prepared using water scavenger compounds [SOCl2 or (Ac)2O] under oxidising conditions, resulting in two-electron (or one-electron, respectively) oxidized cluster units with respect to the starting material [Nb6Cl14(H2O)4] · 4H2O. Of five members of this group single-crystal X-ray structures were determined. The cluster anions exist in all structures as discrete units. The acidic H atoms of all N-bases are hydrogen bonded to H acceptors, in 4 cases to outer, exo bonded Cl atoms of the cluster unit and in one case to the O atom of a co-crystallized THF molecule. In [TMGu-H]2[Nb6Cl18] chains of cluster anions exist hydrogen-bonded through bridging [TMGu-H]+ cations. ESI mass spectra of [MIm-H]2[Nb6Cl18] · 2SOCl2 and [TMGu-H]2[Nb6Cl18] show the expected isotopic distribution patterns for the anions together with other peaks associated to chloride mass losses and/or reduction processes. 相似文献
39.
40.
Bernhard Westermann Nicole Diedrichs Ralf Krelaus Armin Walter Ina Gedrath 《Tetrahedron letters》2004,45(31):5983-5986
Bicyclic lactams serve as building blocks for the synthesis of conformationally restricted peptides. A route to these building blocks is described. They can serve as cis- and trans-peptide bond surrogates. Due to the de novo synthesis, both enantiomeric forms of these products can be produced. Key steps are a lipase-catalyzed saponification of oximes and a highly diastereoselective cyclization utilizing phenylselenyl bromide. In addition, attachment to a solid support has been achieved. 相似文献