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排序方式: 共有163条查询结果,搜索用时 18 毫秒
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Li W Nelson DP Jensen MS Hoerrner RS Javadi GJ Cai D Larsen RD 《Organic letters》2003,5(25):4835-4837
Imidazo[1,2-a]pyrimidine can be arylated at the 3-position with aryl bromides in the presence of base and a catalytic amount of palladium. This provides an efficient one-step synthesis of 3-arylimidazo[1,2-a]pyrimidines from the unsubstituted heterocycle. [reaction: see text] 相似文献
3.
3-Mercapto-2(1H)-pyridinone (1) can be synthesized in three simple high-yielding steps from readily available 2-tert-butylthiazolo[4,5-b]pyridine (2). Its disodium salt condenses with o-chloronitrobenzene, 2-chloro-3-nitropyridine, and 3-chloro-4-nitropyridine 1-oxide to give respectively 4-azaphenoxathiine (10), 1,6-diazaphenoxathiine (12), and 2,6-diazaphenoxathiine 2-oxide (14) which reduces to 2,6-diazaphenoxathiine (15). The structures of these previously unreported azaphenoxathiine systems were confirmed by assignment of their respective (13)C NMR spectra. 相似文献
4.
Minkov I Gel'mukhanov F Friedlein R Osikowicz W Suess C Ohrwall G Sorensen SL Braun S Murdey R Salaneck WR Agren H 《The Journal of chemical physics》2004,121(12):5733-5739
High-resolution x-ray photoelectron emission (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectra of naphthalene are analyzed in terms of the initial state chemical shifts and the vibrational fine structure of the excitations. Carbon atoms located at peripheral sites experience only a small chemical shift and exhibit rather similar charge-vibrational coupling, while the atoms in the bridging positions differ substantially. In the XPS spectra, C-H stretching modes provide important contributions to the overall shape of the spectrum. In contrast, the NEXAFS spectrum contains only vibrational progressions from particular C-C stretching modes. The accuracy of ab initio calculations of absolute electronic transition energies is discussed in the context of minute chemical shifts, the vibrational fine structure, and the state multiplicity. 相似文献
5.
Vasily S. Minkov Evgeny A. Kapustin Elena V. Boldyreva 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(4):416-420
The title compound, betaine 0.77‐perhydrate 0.23‐hydrate, (CH3)3N+CH2COO−·0.77H2O2·0.23H2O, crystallizes in the orthorhombic noncentrosymmetric space group Pca21. Chiral molecules of hydrogen peroxide are positionally disordered with water molecules in a ratio of 0.77:0.23. Betaine, 2‐(trimethylazaniumyl)acetate, preserves its zwitterionic state, with a positively charged ammonium group and a negatively charged carboxylate group. The molecular conformation of betaine here differs from the conformations of both anhydrous betaine and its hydrate, mainly in the orientation of the carboxylate group with respect to the C—C—N skeleton. Hydrogen peroxide is linked via two hydrogen bonds to carboxylate groups, forming infinite chains along the crystallographic a axis, which are very similar to those in the crystal structure of betaine hydrate. The present work contributes to the understanding of the structure‐forming factors for amino acid perhydrates, which are presently attracting much attention. A correlation is suggested between the ratio of amino acid zwitterions and hydrogen peroxide in the unit cell and the structural motifs present in the crystal structures of all currently known amino acids perhydrates. This can help to classify the crystal structures of amino acid perhydrates and to design new crystal structures. 相似文献
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7.
Daniel D. Stöbener Dorian Donath Marie Weinhart 《Journal of polymer science. Part A, Polymer chemistry》2018,56(21):2496-2504
Low-molecular weight linear poly(glycidyl ether)s are typically synthesized via the “classical,” oxy-anionic ring-opening polymerization (ROP) of glycidyl ether monomers at elevated temperatures. To reduce reaction times, a fast process was developed to synthesize oligo(glycidyl ether)s (OGEs) in bulk at a gram-scale utilizing microwave heating. Well-defined thermoresponsive copolymers comprising glycidyl methyl ether and ethyl glycidyl ether with molecular weights of up to 3 kDa were synthesized via microwave-assisted ROP with reaction times of approximately 10 min. The fast reaction kinetics were attributed to the rapid and uniform heating and high temperatures reached during the reaction. Consequently, no significant microwave-specific acceleration of the oxy-anionic ROP was observed. The temperature-triggered phase transition of the OGEs in aqueous solution revealed cloud point temperatures that are highly dependent on the OGE molecular weight, concentration, and comonomer composition, which extends previously reported data. Furthermore, oligo(glycidyl ether) acrylates (OGEAs) with reactive, functional end groups were directly accessible via in situ quenching of the anionic, microwave-assisted ROP with acrylic acid chloride. The obtained thermoresponsive OGEA macromonomers represent a promising material for the functionalization of surfaces via radical grafting methods to obtain functional, thermoresponsive coatings with potential application in cell culture. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2496–2504 相似文献
8.
The study of the planar collisions of a rigid two-link chain with an external surface is presented. There are two points of contact during the impact process with friction, one for each link. For the normal impact, a nonlinear collision force is employed for the elasto-plastic deformation, and the Coulomb’s law models the frictional effects. The impact of the chain is studied numerically, and the results are compared with experiment data obtained from a high-speed camera. Special attention is given to simultaneous impact, slippage, and rebounds at the contact points. 相似文献
9.
Andreas Dorian Emily J. Landgreen Hayley R. Petras Prof. James J. Shepherd Prof. Florence J. Williams 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(42):10839-10843
The facile production of ArCF2X and ArCX3 from ArCF3 using catalytic iron(III)halides is reported, which constitutes the first iron-catalyzed halogen exchange for non-aromatic C−F bonds. Theoretical calculations suggest direct activation of C−F bonds by iron coordination. ArCX3 and ArCF2X products of the reaction are synthetically valuable due to their diversification potential. In particular, chloro- and bromodifluoromethyl arenes (ArCF2Cl, ArCF2Br respectively) provide access to a myriad of difluoromethyl arene derivatives (ArCF2R). To optimize for mono-halogen exchange, a statistical method called Design of Experiments was used. Optimized parameters were successfully applied to electron rich and electron deficient aromatic substrates, and to the late stage diversification of flufenoxuron, a commercial insecticide. These methods are highly practical, being run at convenient temperatures and using inexpensive common reagents. 相似文献
10.
Paul Kautny Dorian Bader Dr. Berthold Stöger Prof. Dr. Georg A. Reider Prof. Dr. Johannes Fröhlich Dr. Daniel Lumpi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(52):18887-18898
To shed light on intramolecular charge‐transfer phenomena in 1,2,3‐triazole‐linked materials, a series of 1,2,3‐triazole‐linked push–pull chromophores were prepared and studied experimentally and computationally. Investigated modifications include variation of donor and/or acceptor strength and linker moiety as well as regioisomers. Photophysical characterization of intramolecular charge‐transfer features revealed ambipolar behavior of the triazole linker, depending on the substitution position. Furthermore, non‐centrosymmetric materials were subjected to second‐harmonic generation measurements, which revealed the high nonlinear optical activity of this class of materials. 相似文献