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991.
Fluorous chiral BINOLs and BINAP were prepared and used as the ligands for an asymmetric addition of Et2Zn to aromatic aldehydes and an asymmetric Heck reaction, respectively. The enantioselectivities were similar in homogeneous system to those of the original non-fluorous reactions. Consecutive reactions were examined by utilizing fluorous–organic biphase and fluorous solid phase extraction techniques. Enantioselectivities in consecutive reactions were close to that attained in the non-fluorous system. The solid phase extraction method also enabled us to perform a simultaneous screening procedure. 相似文献
992.
993.
Y. Mera 《Surface science》2007,601(22):5207-5211
Reversible polymerization and depolymerization reactions of fullerene (C60) molecules are induced by tunnel injection of holes from tips of scanning tunneling microscopes similarly to the reactions induced by tunneling electrons. The bi-directional and bi-polar features of the hole-induced and electron-induced reactions can be interpreted by a unified model considering ionic reactions over symmetry-imposed barriers in the [2+2] cyclo-addition and the reverse reactions. 相似文献
994.
On the Influence of Chemical Transport on the Habit of Crystals The chemical transport of silicon with silicon tetrachloride as transporting agent leads to crystals with octahedral shape. On the other hand in the presence of adsorbable impurities the transported silicon crystallizes in the shape of long needles. Chemical transport reactions of tellurium are successful with iodine or sulphur. The presence of adsorbable transporting agents has considerable influence on the habit of crystals. 相似文献
995.
L.P. Kaptari B. Kämpfer S.S. Semikh S.M. Dorkin 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):119-132
The exclusive charge exchange reaction pD↦n(pp) at intermediate and high energies is studied within the Bethe-Salpeter formalism. The final-state interaction in the detected
pp pair at nearly zero excitation energy is described by the 1
S
0 component of the Bethe-Salpeter amplitude. Results of numerical calculations of polarization observables and differential
cross-section persuade that, as in the non-relativistic case, this reaction i) can be utilized as a “relativistic deuteron
polarimeter” and ii) delivers further information about the elementary nucleon-nucleon charge exchange amplitude.
Received: 26 November 2002 / Accepted: 30 January 2003 / Published online: 29 April 2003 相似文献
996.
997.
The process of planar detonation ignition, induced by a constant-velocitypiston or equivalently by a shock reflected from a stationarywall, is investigated using high-resolution one-dimensionalnumerical simulations. The standard one-step model with Arrheniuskinetics, which models thermally sensitive explosives, is employed.Emphasis is on comparing and contrasting the results of thefinite activation temperature simulations with high activationtemperature asymptotic predictions and previous simulations.During the induction phase, it is shown that the asymptoticresults give qualitatively good predictions. However, for parametersrepresentative of gaseous explosives, subsequent to thermalrunaway at the piston and the formation of a reaction wave,the high activation temperature asymptotic theory is qualitativelyincorrect for moderately high activation temperatures. It isshown that the results are very sensitive to the value of theactivation temperature, especially the distance from the pistonat which a secondary shock forms and the degree of unsteadinessin the reaction wave which moves away from the piston. The dependenceof the ignition evolution on the other parameters (initial shockMach number, heat of reaction and polytropic index) is alsoinvestigated. It is shown that qualitative predictions regardingthe dependence of the ignition evolution on each of the parameterscan be elucidated from finite activation temperature homogeneousexplosion calculations together with the high activation temperatureasymptotic shock ignition results. It is found that for sufficientlystrong initiating shocks the ignition evolution is qualitativelydifferent from cases studied previously in that no secondaryshock forms. For a high polytropic index, corresponding to asimple equation of state model for condensed phase explosives,the results are in much better qualitative agreement with theasymptotic theory. 相似文献
998.
Jairo Quijano Jorge David Claudia Snchez Elizabeth Rincon Doris Guerra Luis A. Len Rafael Notario Jos L. Abboud 《Journal of Molecular Structure》2002,580(1-3):201-205
Thermolysis studies of β-hydroxyolefins in gas phase were realized using ab initio MP2 and DFT methods at the 6-31G* levels to explore the possibility of determining a possible concerted process with a six-membered cyclic transition state (TS). Vibrational frequency calculations were carried out in order to confirm the stationary states, including TS structures. IRC calculations have been performed in all cases in order to verify that localized TS structures connect with the corresponding minimum stationary points associated with the reactant and products. With the aim of corroborating the postulated mechanism in the experimental study, we present a theoretical study in order to calculate the rate constants and the activation parameters. The results obtained are in accordance with the experimental conclusions. 相似文献
999.
A study of the free racinoal reaction of vinylcycloprelpane mediated by p-toluenesulfonyl chloride is described. 相似文献
1000.
J. Ahrens S. Altieri J. R. M. Annand H. -J. Arends R. Beck A. Braghieri N. d'Hose H. Dutz S. Goertz P. Grabmayr S. Hasegawa E. Heid H. Holvoet L. Van Hoorebeke N. Horikawa T. Iwata O. Jahn P. Jennewein R. Kondratiev J. Krimmer M. Lang B. Lannoy K. Livingston J. C. McGeorge W. Meyer A. Panzeri P. Pedroni T. Pinelli I. Preobrajenski G. Reicherz G. Rosner M. Rost T. Rostomyan D. Ryckbosch M. Schumacher B. Seitz G. Tamas A. Thomas R. van de Vyver Th. Walcher F. Zapadtka 《The European Physical Journal A - Hadrons and Nuclei》2005,26(1):135-140
The G asymmetry of the γp↦Nπ reaction has been measured for the first time for Eγ = 340±14 MeV. This observable, for which very scarce published data exist, plays an important role to disentangle the contributions
of the various nucleon resonances. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector system, a linearly
polarized, tagged photon beam, and a longitudinally polarized proton target. 相似文献