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991.
Ras RH Ruotsalainen T Laurikainen K Linder MB Ikkala O 《Chemical communications (Cambridge, England)》2007,(13):1366-1368
Long hollow inorganic nanoparticle nanotubes have been synthesized by templating of block copolymer electrospun fibers with clay mineral platelets followed by interlinking of the platelets using condensation reactions. 相似文献
992.
Gilroy JB Ferguson MJ McDonald R Patrick BO Hicks RG 《Chemical communications (Cambridge, England)》2007,(2):126-128
Formazans react with boron triacetate to produce boratatetrazines, which can be reduced to yield borataverdazyl radical anions--the first boron containing verdazyl radicals. 相似文献
993.
Complexes in which a sigma-H--E bond (E=H, B, Si, C) acts as a two-electron donor to the metal center are called sigma complexes. Clues that it is possible to interconvert sigma ligands without a change in oxidation state derive from C--H activation reactions effecting isotope exchange and from dynamic rearrangements of sigma complexes (see Frontispiece). Through these pathways, metathesis of M--E bonds can occur at late transition metals. We call this process sigma-complex-assisted metathesis, or sigma-CAM, which is distinct from the familiar sigma-bond metathesis (typical for d(0) metals and requiring no intermediate) and from oxidative-reductive elimination mechanisms (inherently requiring intermediates with changed oxidation states and sometimes involving sigma complexes). There are examples of sigma-CAM mechanisms in catalysis, especially for alkane borylation and isotope exchange of alkanes. It may also occur in silylation and alkene hydrogenation. 相似文献
994.
Harris RK Cadars S Emsley L Yates JR Pickard CJ Jetti RK Griesser UJ 《Physical chemistry chemical physics : PCCP》2007,9(3):360-368
The (13)C CPMAS spectrum is presented for the polymorph of oxybuprocaine hydrochloride which is stable at room temperature, i.e. Mod. II degrees . It shows crystallographic splittings arising from the fact that there are two molecules, with substantially different conformations, in the asymmetric unit. An INADEQUATE two-dimensional experiment was used to link signals for the same independent molecule. The chemical shifts are discussed in relation to the crystal structure. Of the four ethyl groups attached to NH(+) nitrogens, one gives rise to unusually low chemical shifts, very different from those of the other three ethyl groups. This is attributed empirically to gamma-gauche conformational effects, as is confirmed by shielding computations. These considerations allow (13)C signals to be assigned to specific carbons in the two crystallographically inequivalent molecules in the crystal structure. Indeed, information about the conformations is inherent in the NMR spectrum, which thus provides data of crystallographic significance. A (13)C/(1)H HETCOR experiment enabled resolution to be obtained in the (1)H dimension and allowed (1)H and (13)C signals for the same independent molecule to be linked. 相似文献
995.
Time resolved gas-phase kinetic studies have contributed a great deal of fundamental information about the reactions and reactivity of heavy carbenes (silylenes, germylenes and stannylenes) during the past two decades. In this article we trace the development of our understanding through the mechanistic themes of intermediate complexes, third body assisted associations, catalysed reactions, non-observed reactions and substituent effects. Ab initio (quantum chemical) calculations have substantially assisted mechanistic interpretation and are discussed where appropriate. Trends in reactivity are identified and some signposts to future studies are indicated. This review, although detailed, is not comprehensive. 相似文献
996.
Time-resolved kinetic studies of the reaction of silylene, SiH2, generated by 193 nm laser flash photolysis of silacyclopent-3-ene, have been carried out in the presence of ammonia, NH3. Second order kinetics were observed. The reaction was studied in the gas phase at 10 Torr total pressure in SF6 bath gas at each of the three temperatures, 299, 340 and 400 K. The second order rate constants (laser pulse energy of 60
mJ +) fitted the Arrhenius equation:noindent Experiments at other pressures showed that these rate constants were unaffected by pressure in the range 10–100 Torr,
but showed small decreases in value at 3 and 1 Torr. There was also a weak intensity dependence, with rate constants decreasing
at laser pulse energies of 30 mJ +. Ab initio calculations at the G3 level of theory, show that SiH2+NH3 should form an initial adduct (donor-acceptor complex), but that energy barriers are too great for further reaction of the
adduct. This implies that SiH2+NH3 should be a pressure dependent association reaction. The experimental data are inconsistent with this and we conclude that
SiH2 decays are better explained by reaction of SiH2 with the amino radical, NH2, formed by photodissociation of NH3 at 193 nm. The mechanism of this previously unstudied reaction is discussed. 相似文献
997.
Multiphoton ionization and electron recombination processes are studied in argon using coherent microwave Rayleigh scattering from a localized, resonance-enhanced multiphoton ionization produced plasma. A time dependent one-dimensional plasma dynamic model is developed to predict the time evolution of the microwave scattering from the plasma. Experimental results of the argon ionization spectrum and electron recombination rates are in good agreement with the model predictions. 相似文献
998.
A three-dimensional model of the forward propagation of nonlinear sound beams in inhomogeneous media, a generalized Khokhlov-Zabolotskaya-Kuznetsov equation, is described. The Texas time-domain code (which accounts for paraxial diffraction, nonlinearity, thermoviscous absorption, and absorption and dispersion associated with multiple relaxation processes) was extended to solve for the propagation of nonlinear beams for the case where all medium properties vary in space. The code was validated with measurements of the nonlinear acoustic field generated by a phased array transducer operating at 2.5 MHz in water. A nonuniform layer of gel was employed to create an inhomogeneous medium. There was good agreement between the code and measurements in capturing the shift in the pressure distribution of both the fundamental and second harmonic due to the gel layer. The results indicate that the numerical tool described here is appropriate for propagation of nonlinear sound beams through weakly inhomogeneous media. 相似文献
999.
Oxidative N‐Heterocyclic Carbene‐Catalyzed γ‐Carbon Addition of Enals to Imines: Mechanistic Studies and Access to Antimicrobial Compounds 下载免费PDF全文
Shihu Su Zhichao Jin Yu‐Huang Wang Prof. Dr. Song Yang Lin‐Hong Jin Prof. Dr. Bao‐An Song Prof. Dr. Yonggui Robin Chi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(28):9984-9987
The reaction mechanism of the γ‐carbon addition of enal to imine under oxidative N‐heterocyclic carbene catalysis is studied experimentally. The oxidation, γ‐carbon deprotonation, and nucleophilic addition of γ‐carbon to imine were found to be facile steps. The results of our study also provide highly enantioselective access to tricyclic sulfonyl amides that exhibit interesting antimicrobial activities against X. oryzae, a bacterium that causes bacterial disease in rice growing. 相似文献
1000.