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81.
K. V. Narayana Andreas Martin B. Lücke M. Belmans F. Boers D. van Deynse 《无机化学与普通化学杂志》2005,631(1):25-30
The syntheses of transition metal promoted (M = Co, Cr, Fe, Mo) supported vanadium phosphate (VPO) catalysts (TiO2 (anatase), γ‐Al2O3) and their characterization by N2‐adsorption, X‐ray diffractometry (XRD), FTIR‐spectroscopy and determination of V‐valence state is reported. The catalytic properties were checked in the heterogeneous catalytic ammoxidation of 2, 6‐dichlorotoluene to the corresponding nitrile. The catalyst samples were prepared by synthesis of the precursor compound VOHPO4 · 0.5 H2O, impregnation using various metal salt solutions and mixing with the support materials. The characterization revealed increased surface areas for all the promoted samples in comparison to the basic materials. XRD showed the formation of (VO)2P2O7 after calcinations as well as patterns of support materials (anatase, γ‐Al2O3). The formation of crystalline proportions of mixed oxides were not observed. The catalytic ammoxidation runs revealed a significant effect of the promoter metals on the catalytic properties by an increase of yield by ca. 20 % compared to bulk VPO. Almost complete conversion of 2, 6‐dichlorotoluene and 81 % yield of nitrile were observed using a 25 %VPCoO/γ‐Al2O3 catalyst. 相似文献
82.
Bringmann G Mühlbacher J Reichert M Dreyer M Kolz J Speicher A 《Journal of the American Chemical Society》2004,126(30):9283-9290
Cyclic bisbibenzyls, like isoplagiochins C (1) and D (2), are stereochemically intriguing molecules: Although not equipped with any of the traditional stereogenic elements that render molecules conformationally stable per se, they are sometimes isolated in an optically active form and are thus chiral at room temperature. The paper describes quantum chemical calculations, in particular investigations of the conformational space and molecular dynamics simulations, showing that the helicity is a property of the entire molecule, whose ring strain makes the molecule configurationally stable overall, with (formally) three stereogenic elements (two biaryl axes and one helical stilbene unit). Only one of the biaryl axes (the 'upper' one, joining C-12' and C-14) has a stable configuration, leading to a population of four interconverting diastereomers, yet without racemization at room temperature. On the basis of these conformational and dynamic calculations, the circular dichroism spectrum of isoplagiochin C (1) was calculated, leading to the first assignment of the absolute configuration of a cyclic bisbibenzyl. Accordingly, 1 has the P-configuration at the stereochemically stable biaryl axis and constitutes a mixture of diastereomers with respect to the other biaryl axis and the helical stilbene unit. From the temperature dependence of the racemization rates, an enantiomerization barrier of 101.6 kJ/mol was determined. Likewise, for the first time for cyclic bisbibenzyls, the enantiomeric ratio of this natural product was determined, by chromatography on a chiral phase with CD-coupling. Accordingly, 1 from Plagiochila deflexa is not enantiomerically pure, but occurs in a 85:15 ratio in favor of the enantiomer that has the P-configuration at the stereochemically stable axis. 相似文献
83.
The addition of proton acids as HF, HCl, HBr, HOAc and phenol to alkyne-derivatives of the type (CH3)2N? C?C? CO? R( 1 ) yielding the adducts 2 to 6 is investigated. The stereochemical course of the reaction is mainly influenced by the structure of the alkyne 1 . Kinetic investigations show that the rate of the third-order-reaction increases from 1 a (R?H) to 1 b (R ? CH3) and 1 c (R ? OCH3) and decreases drastically in polar solvents. According to these results a reaction mechanism is outlined and discussed. 相似文献
84.
Winfried Wendelin Hans-Wolfgang Schramm Andreas Blasi-Rabassa 《Monatshefte für Chemie / Chemical Monthly》1985,116(3):385-400
Guanidine and phenylguanidine react with phenylhexadienone1b and 1,5-diaryl-2,4-pentadien-1-ones1c–k respectively (via unstable dihydropyrimidines of type2 as intermediates) to 4-methyl- and 4-aryl-6-styryl-2-pyrimidinamines3b–j and N2-phenyl-2-pyrimidinamines7c, k. Efforts to stabilize the intermediates2 by introduction of electron-withdrawing substituents (compare2,3) were not successful. Similarly, thiourea reacts with diphenylpentadienone1c to afford (via8c) 4-phenyl-6-phenethylpyrimidinethione9c. Action of guanidine on 1,3,5-triphenylpentadienone101 and on the 5-(3-chlorophenyl) analogue10m under decomposition of the ketones yields 4,6-diphenyl-and 4-(3-chlorophenyl)-6-phenyl-2-pyrimidineamine (121 andm), respectively. The formation of12m proves that acetophenone splits off from101,m during the reactions. However, heating of thiourea with10m in sodium butylate/butanol gives the expected 4,6-diphenyl-4-styryldihydropyrimidinethione13m. The reaction of thiourea with triphenylpentadienone101 is taking an atypical course: Addition of thiourea to the δ- and β-carbon atom of101 affords 2-(4,6-diphenyl-2-thioxohexahydro-4-pyrimidinyl)acetophenone (141); the conformation of the latter was deduced from1H-NMR data. 相似文献
85.
Wolfgang?Gutleben Verena?Unterholzner Dietmar?Volgger Andreas?ZemannEmail author 《Mikrochimica acta》2004,146(2):111-117
In the course of this investigation, a method for the characterization and differentiation of paper pulps was developed. After hydrolyzation of the papers and the respective raw pulps with trifluoroacetic acid, the hydrolyzates were analyzed with respect to their carbohydrate composition using ion exchange chromatography. The variations in carbohydrate composition mainly arise from the various hemicelluloses of the papers and pulps. The chromatographic results were then further processed using principal component analysis which allows correlating the various papers to different pulp materials. 相似文献
86.
When crystallized from appropriate solvents, the complex aqua-bis(dimethylglyoximato)nitrocobalt (III) may incorporate solvent molecules, thus forming a variety of mixed crystals. In the resulting host-guest crystals, the space groupP2l/m and the packing motif of the pure host compound are retained. Lattice constantsa andb remain essentially unaltered upon intercalation, whereasc and the monoclinic angle depend largely on the clathrated guest. Space filling and intermolecular contacts are discussed.Dedicated to Professor Peter Paetzold at the occasion of his 60th birthday. A preliminary account of this work has been given at the Spring Meeting of the British Crystallographic Association, Newcastle upon Tyne, 1994. 相似文献
87.
Petra A. M. van Koppen Andreas J. Illies Shuying Liu Michael T. Bowers 《Journal of mass spectrometry : JMS》1982,17(9):399-402
The effect of the precursor ion internal energy on the branching ratios obtained from collision induced dissociation fragmentation patterns was examined for [NH3]+ and [C2H4N]+. The ion internal energy was changed by varying both the chemical ionization reagent gas and the ion source pressure. Effects observed in the collision induced dissociation fragmentation patterns as a function of the ion source pressure are explained by the reaction exothermicities and by collisional deactivation of internally excited ions (at high pressure). 相似文献
88.
Karsten Tillmann Andreas Thust Andreas Gerber Martin P Weides Knut Urban 《Microscopy and microanalysis》2005,11(6):534-544
The structural properties of beta-phase tantalum nanocrystallites prepared by room temperature magnetron sputter deposition on amorphous carbon substrates are investigated at atomic resolution. For these purposes spherical aberration-corrected high-resolution transmission electron microscopy is applied in tandem with the numerical retrieval of the exit-plane wavefunction as obtained from a through-focus series of experimental micrographs. We demonstrate that recent improvements in the resolving power of electron microscopes enable the imaging of the atomic structure of beta-tantalum with column spacings of solely 0.127 nm with directly interpretable contrast features. For the first time ever, we substantiate the existence of grain boundaries of 30 degrees tilt type in beta-Ta whose formation may be well explained by atomic agglomeration processes taking place during sputter deposition. 相似文献
89.
The two bis-macrocycles 4 and 5 in which the tetraaza units are separated by a chain of different length, have been synthesized using 1,4,7-tritosyl-1,4,7,11-tetraazacyclotetradecane as starting compound and bifunctional alkylating agents. The bis-macrocycles give binuclear complexes with Ni2+ and Cu2+, the properties of which have been studied to obtain information about the interaction of the two subunits as a function of the distance. The VIS spectra of the Ni2+ and Cu2+ complexes indicate that both metal ions are in a square-planar geometry as expected from the results of the analogous complexes with 1,4,7,11-tetraazacyclotetradecane 7 . Cyclic voltammetry and differential pulse polarography of the binuclear Ni2+complexes in CH3CN show a single two-electron step for ligand 5 , whereas two distinct one-electron redox processes can be observed for ligand 4 , indicating that the two metal ions interact with each other when the chain length is shorter. Similarly, the EPR studies of frozen solutions of the binuclear Cu2+ complexes clearly show that a magnetic dipolar interaction between the two paramagnetic centers exists, and that the strength of it depends upon the length of the bridge. Finally, from the X-ray structures of the binuclear Ni2+ complexes with 4 and 5 , it is seen that the two rings are kept apart as far as possible, the distances between the two metal ions determined in the solid correlate well with the observations in solution. 相似文献
90.
Three new rigid bridging ligands for metal complexation (7=bmb, 8=bqb and 11=btb) were prepared from a rigid triptycene spacer connected to two bipyridine ligands using a Horner–Emmons type reaction. The triptycene spacer is substituted by methoxy groups in the case of bmb and in the case of bqb by a benzoquinone substituent. The corresponding metal complexes (ruthenium and/or osmium) were synthesised and the different luminescence behaviour was tested. They show great potential for the investigation of intramolecular electron and energy transfer reactions. The dinuclear metal complex Ru---bqb---Os is an interesting system in which the bridging ligand bqb acts as a redox switch, able to tune the conductivity for energy or electrons across the bridge. 相似文献