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91.
The mechanism of the propylene oxidation by Pd(NOn)Cl2 − m(CH3CN)2 complexes (n = 2, 3; m = 0, 1, 2) in chloroform solutions has been studied by 1H NMR and IR spectroscopy. The main reaction products are acetone and 2-nitropropylene, with their ratio depending on the equilibrium existing in the reaction solutions between palladium complexes containing NOn ligands bonded to a palladium atom via either an oxygen or a nitrogen atom. Reactivities of the oxygen bonded nitrato and nitrito complexes are significantly higher than that of the nitrogen bonded nitro complex. Various new organopalladium intermediates have been observed and monitored in situ. A reversible insertion of the coordinated propylene into the Pd-O or Pd-N bonds results in nitrato-, nitrito- and nitropalladation intermediates, which then decompose via a β-hydrogen elimination. Two isomers of the nitritopalladation intermediate have been detected, i.e., a palladium metallacycle and an open ring complex, with the latter being much more reactive towards the β-hydrogen elimination than the former. The decomposition of the nitrato- and nitritopalladation intermediates results in the organometallic precursor of acetone, i.e., an acetonylpalladium complex, and then in acetone itself. On the other hand, the nitropalladation intermediate originates 2-nitropropylene. In the presence of dioxygen, which re-oxidizes the nitrosyl groups, the acetone formation becomes a catalytic reaction with respect to both palladium and nitrogen. 相似文献
92.
Cobas JC Constantino-Castillo V Martín-Pastor M del Río-Portilla F 《Magnetic resonance in chemistry : MRC》2005,43(10):843-848
(1)H NMR scalar coupling constants are a rich source of information on molecular structure, but their extraction from spectra can be less than straightforward. Previous approaches to J extraction include methods proposed by Hoye, Golotvin, and the 'modified J-doubling' method. Here we describe the ACCA method, currently implemented in the NMR package MestReC, which allows a high degree of automation in the extraction of coupling patterns even in the case of complex multiplets with sublinewidth splitting. The new approach is illustrated by application to strychnine, for which it has detected previously unreported couplings. 相似文献
93.
Margiolaki I Margadonna S Prassides K Hansen T Ishii K Suematsu H 《Journal of the American Chemical Society》2002,124(38):11288-11289
The powder neutron diffraction technique has been used for the direct observation of magnetic scattering below a Curie temperature of approximately 14 K in the fullerene-based molecular ferromagnet Eu6C60. Europium is in the divalent state with a magnetic moment of 7.1(3) muB per atom, and the configurational symmetry of the magnetic structure is body-centered cubic. Close contacts between Eu2+ and neighboring C60 units provide the signature of orbital hybridization, which can evidently account for the conducting and magnetic properties of the material. 相似文献
94.
Díez-Barra E García-Martínez JC del Rey R Rodríguez-López J Giacalone F Segura JL Martín N 《The Journal of organic chemistry》2003,68(8):3178-3183
New chiral, soluble binaphthyl derivatives that incorporate stilbenoid dendrons at the 6,6'-positions have been prepared. The synthesis of the new enantiopure dendrimers was performed in a convergent manner by Horner-Wadsworth-Emmons (HWE) reaction of the appropriately functionalized 1,1'-binaphthyl derivative (R)-1 and the appropriate dendrons (R)(2n)G(n)-CHO. Different electroactive units were incorporated in the peripheral positions of the dendrons in order to tune both the optical and electrochemical behavior of these systems. Fluorescence measurements on the chiral dendrimers reveal a strong emission with maxima between 409 and 508 nm depending upon the substitution pattern. Finally, the redox properties of the dendrimers were determined by cyclic voltammetry, showing the influence of the functional groups at the peripheral positions of the dendrimer on the redox behavior of these systems. 相似文献
95.
Castagnola M Zuppi C Rossetti DV Vincenzoni F Lupi A Vitali A Meucci E Messana I 《Electrophoresis》2002,23(12):1769-1778
The general properties of dendrimers and in particular their electrolytic characteristics that are relevant in electrokinetic separations, are described. In order to confirm theoretical considerations on commercial dendrimer charge and hydrodynamic radius, several capillary zone electrophoresis (CZE) experiments were performed. Electrophoretic mobilities measured at different pH values indicated a sensible increase of dendrimer hydrodynamic radius at pH values lower than 2.5. This was probably due to the Coulombic repulsion of charged amine groups of the inner dendrimer shells. The principal reasons that should address the use of dendrimers as pseudostationary phases in micellar electrokinetic chromatography (MEKC) are discussed. Moreover, a survey of different separations performed utilizing dendrimers in MEKC as well as of several future plausible uses of various classes of dendrimers is presented. 相似文献
96.
Giuliana Biagi Irene Giorgi Oreste Livi Clementina Manera Valerio Scartoni Pier Luigi Barili 《Journal of heterocyclic chemistry》1997,34(3):845-851
This paper continues the synthesis of new 1,2,3-triazolo[1,2-a]benzotriazoles or 2,3-benzo-1,3a,6,6a-tetrazapentalenes to submit to biological assays. The derivatives were obtained by deoxycyclization reactions of appropriate nitrophenyl-1,2,3-triazole derivatives and by thermal decomposition of appropriate azidophenyl-1,2,3-triazoles (Schemes 1 and 2). Some attempts to extend these synthetic routes to the preparation of 1,2,4-triazolo[1,2-a]benzotriazoles (Scheme 3) and 1,2,3-triazolo[1,2-b]-4H-1,2,3-benzo-triazines (Scheme 4) completely failed. 相似文献
97.
Karl Krmer Hans U. Güdel Gerd Meyer Thorsten Heuer Norman N. Edelstein Bernd Jung Lukas Keller Peter Fischer Eugeniusz Zych Janusz Drozdzynski 《无机化学与普通化学杂志》1994,620(8):1339-1345
The ternary uranium(III) halides A2UX5 (A = K, Rb; X = Cl, Br, I) have been prepared from the binary components AX and UX3 in sealed tantalum containers. According to their Guinier X-ray powder patterns, they all crystallize with the K2PrCl5/Y2HfS5 type of structure. Lattice constants for ambient temperature are reported. Single-crystal structure refinemens were undertaken for K2UI5 and Rb2UCl5. Magnetic susceptibility data were recorded with a SQUID magnetometer from liquid helium to room temperature. One-dimensional (intrachain) and three-dimensional antiferromagnetic ordering occur at low temperatures dependent upon the U3+? U3+ distance. Absorption spectra were recorded between 4 000 and 28 000 cm?1. They show f—f transitions typical for U3+ and, depending on the halide, very strong f—d transitions above 14 000 to 15 000 cm?1, respectively. 相似文献
98.
99.
J. del Cerro 《Journal of Thermal Analysis and Calorimetry》1988,34(1):335-344
Simultaneous measurement of the influence of the electric field on specific heat, thermal conductivity and pyroelectric coefficient is described as a summary of previous papers. From these coefficients, which are determined by means of a flux calorimeter, the behaviour of other properties, such as thermal diffusivity and electrocaloric coefficient, is deduced.The data are compared with the findings obtained by other authors with traditional methods.
This work has been supported by the Spanish C.A.I.C. y T. 相似文献
Zusammenfassung In Zusammenfassung vorhergehender Arbeiten wurde die simultane Messung des Einflusses von elektrischen Feldern auf spezifische Wärme, Wärmeleitfähigkeit und pyroelektrischen Koeffizienten beschrieben. Auf Grundlage dieser Konstanten, die mittels eines Fluxkalorimeters bestimmt wurden, konnte das Verhalten anderer Eigenschaften wie z. B. thermische Diffusionskonstante und elektrokalorischer Koeffizient abgeleitet werden. Die Daten wurden mit durch herkömmliche Methoden erhaltenen Ergebnissen anderer Autoren verglichen.
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This work has been supported by the Spanish C.A.I.C. y T. 相似文献
100.
del Mar Conejo M Fernández R del Río D Carmona E Monge A Ruiz C Márquez AM Sanz JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(18):4452-4461
The beryllocenes [Be(C(5)Me(4)H)(2)] (1), [Be(C(5)Me(5))(2)] (2), and [Be(C(5)Me(5))(C(5)Me(4)H)] (3) have been prepared from BeCl(2) and the appropriate KCp' reagent in toluene/diethyl ether solvent mixtures. The synthesis of 1 is facile (20 degrees C, overnight), but generation of decamethylberyllocene 2 demands high temperatures (ca. 115 degrees C) and extended reaction times (3-4 days). The mixed-ring beryllocene 3 is obtained when the known [(eta(5)-C(5)Me(5))BeCl] is allowed to react with K[C(5)Me(4)H], once more under somewhat forcing conditions (115 degrees C, 36 h). The structures of the three metallocenes have been determined by low-temperature X-ray studies. Both 1 and 3 present eta5/eta1 geometries of the slip-sandwich type, whereas 2 exhibits an almost regular, ferrocene-like, sandwich structure. In the mixed-ring compound 3, C(5)Me(5) is centrally bound to beryllium and the eta(1)-C(5)Me(4)H ring bonds to the metal through the unique CH carbon atom. This is also the binding mode of the eta(1)-ring of 1. To analyze the nature of the bonding in these molecules, theoretical calculations at different levels of theory have been performed on compounds 2 and 3, and a comparison with the bonding in [Be(C(5)H(5))(2)] has been made. As for the latter molecule, energy differences between the eta5/eta5 and the eta5/eta1 structures of 2 are very small, being of the order of a few kcal mol(-1). Constrained space orbital variations (CSOV) calculations show that the covalent character in the bonding is larger for [Be(C(5)Me(5))(2)] than for [Be(C(5)H(5))(2)] due to larger charge delocalization and to increased polarizability of the C(5)Me(5) fragment. 相似文献