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Ionel I Mangalagiu Geanina C MangalagiuCalin Deleanu Gabi DrochioiuMagda Ghe Petrovanu 《Tetrahedron》2003,59(1):111-114
The ability of 4-methylpyrimidinium ylides (as 1,3-dipoles) to react with activated non-symmetrical substituted dipolarophiles (alkenes and alkynes) is presented. 4-Methylpyrimidinium ylides did not react with alkenes. With alkynes the reactions are regiospecific, a single regioisomer being obtained. A possible mechanism for the reaction pathway is proposed. For the first time in the pyrimidinium ylides series both isomers resulting from bonding to the 2-and 6-positions of the heterocycle ring were obtained. The appropriate conditions in order to increase the selectivity of one of the isomers were determined. 相似文献
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Ireland T Tappe K Grossheimann G Knochel P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(4):843-852
A new family of ferrocenylphosphane ligands has been prepared. Their flexible synthesis allows many structural modifications. The asymmetric induction of these ligands was examined in the hydrogenation of functionalized C=C, C=O, and C=N bonds. The enantioselectivity of the reaction was strongly dependent on the substituent R at the position alpha to the ferrocene moiety. In many cases, both enantiomeric beta-hydroxyesters of the reduction product can be obtained by simply replacing a dimethylamino group in the ligand with a methyl group. 相似文献
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Neta Shefer 《Tetrahedron letters》2007,48(46):8178-8181
Thiols and disulfides are oxidized to the corresponding sulfonic and sulfinic acids using HOF·CH3CN. This oxidation is suitable for a variety of thiols and disulfides and proceeds under mild conditions, in short reaction times and with high yields. 相似文献
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Russian Physics Journal - Results of calculation of the transmission function for ensembles of ice crystals typical of crystal clouds are presented as functions of the wave numbers. Considering... 相似文献
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Shock waves in saturated thermoelastic porous media 总被引:1,自引:0,他引:1
The objective of this paper is to develop and present the macroscopic motion equations for the fluid and the solid matrix, in the case of a saturated porous medium, in the form of coupled, nonlinear wave equations for the fluid and solid velocities. The nonlinearity in the equations enables the generation of shock waves. The complete set of equations required for determining phase velocities in the case of a thermoelastic solid matrix, includes also the energy balance equation for the porous medium as a whole, as well as mass balance equations for the two phase. In the special case of a rigid solid matrix, the wave after an abrupt change in pressure propagates only through the fluid. 相似文献
8.
K. I. Shefer S. V. Cherepanova S. V. Tsybulya V. P. Isupov È. M. Moroz 《Journal of Structural Chemistry》2013,54(4):730-740
Using the simulation method for the diffraction patterns of one-dimensionally disordered materials, the effect of different violations in the layered structure of aluminum trihydroxides (gibbsite and bayerite) on their diffraction patterns is analyzed. The features of the diffraction patterns of a disordered gibbsite sample obtained by intercalation-deintercalation of lithium salts are considered. 相似文献
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The two-layer flows of a liquid and a gas in a horizontal channel are investigated under condition of given gas flow rate. Evaporation on the thermocapillary interface is taken into account. An exact solution is constructed of the Navier–Stokes equations in the Boussinesq approximation, taking into account the Dufour effect in the gas-vapor layer. Within the framework of linear theory, the stability of the obtained solutions and the characteristics of the arising perturbations are studied. The influence is considered of the thickness of the liquid layer and the magnitude of the longitudinal temperature gradient on the structure of the basic flow and perturbations. 相似文献
10.
Asymptotic Behavior of the Mean Sojourn Time for a Random Walk to be in a Domain of Large Deviations
Siberian Advances in Mathematics - We study the asymptotic behavior of the mean of sojourn time for a homogeneous random walk defined on $$ [0,n]$$ to be above a receding curvilinear boundary in a... 相似文献