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81.
An expeditious synthetic method for the preparation of bis(indollyl)methane derivatives has been developed through a bismuth nitrate-catalyzed reaction of indole with various carbonyl compounds in mortar and pastle under solvent-free conditions. 相似文献
82.
Alternating copolymers of vinyl acetate (VAc) and maleic anhydride (MA) are produced preferentially when VAc and MA are copolymerized at moderate temperatures while random copolymers are produced at temperatures above 90°C. A charge-transfer complex (CTC) of VAc/MA exists at moderate temperatures but does not exist at temperatures above 90°C. 相似文献
83.
Dolores Bellido-Milla Laura Ma Cubillana-Aguilera Mohammed El Kaoutit Ma Purificación Hernández-Artiga José Luis Hidalgo-Hidalgo de Cisneros Ignacio Naranjo-Rodríguez José Ma Palacios-Santander 《Analytical and bioanalytical chemistry》2013,405(11):3525-3539
Graphite powder-based electrodes have the electrochemical performance of quasi-noble metal electrodes with intrinsic advantages related to the possibility of modification to enhance selectivity and their easily renewable surface, with no need for hazardous acids or bases for their cleaning. In contrast with commercial electrodes, for example screen-printed or sputtered-chip electrodes, graphite powder-based electrodes can also be fabricated in any laboratory with the form and characteristics desired. They are also readily modified with advanced materials, with relatively high reproducibility. All these characteristics make them a very interesting option for obtaining a large variety of electrodes to resolve different kinds of analytical problems. This review summarizes the state-of-the-art, advantages, and disadvantages of graphite powder-based electrodes in electrochemical analysis in the 21st century. It includes recent trends in carbon paste electrodes, devoting special attention to the use of emergent materials as new binders and to the development of other composite electrodes. The most recent advances in the use of graphite powder-modified sol–gel electrodes are also described. The development of sonogel–carbon electrodes and their use in electrochemical sensors and biosensors is included. These materials extend the possibilities of applications, especially for industrial technology-transfer purposes, and their development could affect not only electroanalytical green chemistry but other interesting areas also, for example catalysis and energy conversion and storage. 相似文献
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Dr. Laura Orian Lando P. Wolters Prof. Dr. F. Matthias Bickelhaupt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(40):13337-13347
A mechanistic density functional theory study of acetylene [2+2+2] cyclotrimerization to benzene catalyzed by RhI half metallocenes is presented. The catalyst fragment contains a heteroaromatic ligand, that is, the 1,2‐azaborolyl (Ab) or the 3a,7a‐azaborindenyl (Abi) anions, which are isostructural and isoelectronic to the hydrocarbon cyclopentadienyl (Cp) and indenyl (Ind) anions, respectively, but differ from the last ones on having two adjacent carbon atoms replaced with a boron and a nitrogen atom. The better performance of either the classic hydrocarbon or the heteroaromatic catalysts is found to depend on the different mechanistic paths that can be envisioned for the process. The present analyses uncover and explain general structure–reactivity relationships that may serve as rational design principles. In particular, we provide evidence of a reverse indenyl effect. 相似文献
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Prof. Dr. Javier A. Cabeza Dr. Pablo García-Álvarez Prof. Dr. Mar Gómez-Gallego Laura González-Álvarez Alba D. Merinero Prof. Dr. Miguel A. Sierra 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(36):8635-8642
The reactivity of amidinatotetrylenes of the type E(tBu2bzm)R1 (E=Si, Ge; tBu2bzm=N,N′-bis(tertbutyl)benzamidinate; R1=alkyl or aryl) with the chromium Fischer alkynylcarbene complexes [Cr{C(OEt)C2R2}(CO)5] (R2=Ph; ferrocenyl, Fc) has been studied. At room temperature, two different reaction pathways have been identified: (a) attack of the amidinatotetrylene to the alkynyl C2 atom (γ-attack), which leads to σ-allenyl complexes in which the original Ccarbene atom maintains its attachment to the Cr(CO)5 and OEt groups (compounds 3 ), and (b) attack of the amidinatotetrylene to the Ccarbene atom (α-attack), which ends in σ-allenyl complexes in which the original Ccarbene atom is not attached to the metal atom and has been inserted into an E−N bond of the amidinatotetrylene forming an E-C-N-C-N five-membered ring (compounds 4 ). It has been found that compounds 3 are thermodynamically less stable than their corresponding 4 isomers and that some of the former (E=Ge; R1=CH2SiMe3) can be transformed into the latter upon heating. At high temperatures (>70 °C) the reactions involving bulky amidinatotetrylenes (R1=Mes, tBu) end in the carbene-substitution products [Cr{E(tBu2bzm)R1}(CO)5]. 相似文献
89.
In this paper, it is considered the inverse kinematics problem, which is faced from a differential point of view. In particular, it is shown that an asymptotic inverse kinematics can be interpreted as a Lie symmetry of the direct kinematics. A parameterization of all Lie symmetries of the direct kinematics is proposed, and the classical Newton and gradient method are obtained as particular cases. 相似文献
90.
A Roe‐type decomposition for a system of equations governing onshore/offshore wave transformation in coastal waters is derived. The equation set approximated pertains to coastal waters prior to wave breaking, and is based on depth‐averaging and time‐averaging of the Euler equations. The equations are those used in many commercial codes for simulation of wave height and wave‐averaged currents. This novel approach uses a combination of some standard Roe averages, together with physical reasoning and power series expansions to derive a Roe‐averaged Jacobian (with real, linearly independent eigenvectors) and ensures conservation, and thereby effects the decomposition. It is shown that the resulting derived Roe‐averaged quantities are accurate to a high degree, by comparing them with their analytical equivalents for a wide range of nondimensional water depths and slopes likely to be encountered in coastal problems. Numerical tests of time‐invariant wave height transformation and wave group propagation are undertaken; these indicate good performance of the scheme in practice. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献