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991.
Spies P Fröhlich R Kehr G Erker G Grimme S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(1):333-343
The series of phosphine-borane adducts, Ph2(H3C--C[triple chemical bond]C)P--B(C6F5)3 (8 c), Ph(H3C--C[triple chemical bond]C)2P--B(C6F5)3 (8 b) and (H3C--C[triple chemical bond]C)3P--B(C6F5)3 (8 a), was prepared. The X-ray crystal structure analyses revealed close to eclipsed conformations for all members of this series with average dihedral angles theta(C-P-B-C) of 8.1 degrees (8 c), 12.3 degrees (8 b) and 20.3 degrees (8 a). Quantum chemical analysis of these compounds revealed the importance of a subtle interplay between competing attractive and repulsive secondary interactions, causing the surprising eclipsed conformational preference for systems of this degree of complexity. Some cyclic phosphine-borane adducts were studied for comparison. 相似文献
992.
993.
N-K electron energy-loss near-edge structures for TiN/VN layers: an ab initio and experimental study
Lazar P Redinger J Strobl J Podloucky R Rashkova B Dehm G Kothleitner G Sturm S Kutschej K Mitterer C Scheu C 《Analytical and bioanalytical chemistry》2008,390(6):1447-1453
We study N-K-edge electron energy-loss near-edge structures for well-defined TiN/VN bilayers grown on a MgO(100) substrate
by both calculations and experiments. The structural relaxations and the electronic structure of TiN/VN multilayers are calculated
using the Vienna Ab Initio Simulation Package computer code, which uses density functional theory to describe the electronic
interaction. The effects of the core hole created in the excitation process are included in the calculations. For VN, off-stoichiometric
effects due to nitrogen vacancies are modelled. The partial density of states (PDOS) for the N-K edge of atoms in the vicinity
of the TiN/MgO interface revealed that two new peaks appear between 7 and 9 eV instead of a broad shoulder typical for the
bulk. For the VN/TiN interface, the PDOS is modified only slightly, owing to similar bonding on both sides of the interface,
and is thus very similar to the respective bulk spectra. An experimental spectrum taken at the VN/TiN interface is, however,
well described by an average of the simulated spectra for VN and TiN bulk (interface). Such a finding is characteristic of
an intermixed interface.
相似文献
994.
995.
Spannhoff K Kehr G Kehr S Fröhlich R Erker G 《Dalton transactions (Cambridge, England : 2003)》2008,(25):3339-3344
Staudinger reaction of dppm-CN (5) gave the corresponding bis(N-phenylphosphinimino)acetonitrile system (6). Deprotonation with LDA furnished the corresponding anionic ligand 9. Its reaction with [(CO)(2)RhCl](2) gave the corresponding kappa(2)N,N'-chelate complex 11. X-Ray diffraction revealed a non-planar boat-like conformation of the six-membered chelate ring in the crystal. Treatment of 9 with [(nbd)RhCl](2) gave the six-membered chelate complex 12 which features a different twist-like structure in the solid state, as does 13, which was formed by reacting 9 with [(cod)IrCl](2). 相似文献
996.
997.
A Michael addition of allenoates to electron-deficient olefins was mediated efficiently by a catalytic amount of commercial tetra-n-butylammonium fluoride (TBAF) under mild conditions. And 2-alkynyl substituted glutaric acid derivatives, which may be potential building blocks in organic synthesis, were obtained in good to excellent yields from these reactions. The mechanism for the Michael addition reaction may involve the formation of an alkynylenolate intermediate. 相似文献
998.
Mohr GJ Müller H Bussemer B Stark A Carofiglio T Trupp S Heuermann R Henkel T Escudero D González L 《Analytical and bioanalytical chemistry》2008,392(7-8):1411-1418
Eight new acidochromic dyes have been synthesised that can be used for optically monitoring pH in the range from 3 to 12. Their corresponding pK(a) values have been both measured and calculated theoretically by means of density functional theory. The synthesis of these new dyes is facile without the need for chromatographic purification. The dyes can be covalently linked to polymers containing hydroxyl functions such as cellulose, polyurethane hydrogel, and hydroxyalkyl methacrylate. The resulting sensor layers exhibit significant colour changes both in the UV and in the visible spectral range. 相似文献
999.
Chiral separation by capillary electromigration techniques 总被引:1,自引:0,他引:1
This review gives an overview of chiral separation principles and their applications in capillary electromigration techniques. The basic chiral separation principles are explained and the mechanisms discussed. Recent developments and new techniques in CZE and capillary electrochromatography (CEC) are highlighted. New chiral selectors among cyclodextrins, crown ethers, carbohydrates, macrocyclic antibiotics, proteins, chiral ion-pairing reagents, chiral surfactants and chiral metal ion complexes and their chiral recognition ability are discussed. Recent advances in chip technology for chiral separation and new approaches regarding improvement of detection sensitivity are presented. Due to the tremendous number of publications dealing with applications, in this review only recent applications are summarized. 相似文献
1000.
The iodocyclization of gem-difluorohomoallenyl and gem-difluorohomopropargyl alcohols with I2 and ICl, respectively, produced the corresponding fluorinated iodofuran analogues in good yields. The iodo substituent in fluorinated 4-iodofurans was utilized as a synthetic handle to prepare multi-substituted 3-fluorofurans using a Suzuki cross-coupling reaction. The yields of both iodocyclization of gem-difluorohomopropargyl alcohol and subsequent Suzuki coupling were dramatically enhanced by microwave irradiation. 相似文献