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941.
Jacob LA Matos B Mostafa C Rodriguez J Tillotson JK 《Molecules (Basel, Switzerland)》2004,9(8):622-626
Benzyl selenocyanates can be made from the corresponding benzylic bromides or chlorides in 30-60 minutes using acetonitrile as a solvent. The products may be obtained pure in satisfactory yields without recourse to chromatography. 相似文献
942.
This paper deals with the problem of heating a finite slab using laser radiation in relation to the parameters characterizing the laser pulse, namely: qmax(W/m2), the maximum laser power density, t0 the time interval required to reach qmax and td, the pulse time duration. The pulse shape q(t) is suggested in the form: q(t)=βqmax(t/td)(1-(t/td))exp-B(t-t0/td), where β and B are parameters. Fitting with published experimental pulse [Ready JF. Effects due to absorption of laser radiation. J Appl Phys 1965;36:462–68] is made. Fourier series expansion technique is considered to solve the problem. The critical time required to initiate melting tm is estimated for four metallic elements and five semiconductors, namely: Al, Cu, Ag, Au (aluminum, copper, silver, and gold), cadmium sulfide, germanium, silicon, alpha beryllium oxide, and silicon carbide. Five pulses with different characteristic parameters are considered.Computations revealed that the thermal response of the targets is highly affected by qmax and to, while the pulse time duration is less effective in determining the value of tm. Moreover, it is revealed that the relation between tm and the melting temperature for the same laser pulse is nonlinear for the considered targets under the indicated conditions. 相似文献
943.
Basset JM Copéret C Lefort L Maunders BM Maury O Le Roux E Saggio G Soignier S Soulivong D Sunley GJ Taoufik M Thivolle-Cazat J 《Journal of the American Chemical Society》2005,127(24):8604-8605
Alkane metathesis, a reaction catalyzed by the silica-supported tantalum hydride [(SiO)2Ta-H], 1, which transforms acyclic alkanes into their higher and lower homologues, was reported in 1997. New studies conducted in a continuous flow reactor in the case of propane indicate that, by varying the contact time, hydrogen and olefins are primary products. This crucial observation, as well as the known properties of tantalum alkyls to perform alpha-H or beta-H eliminations, supports the proposition of a new mechanism involving metallacyclobutane intermediates just like in olefin metathesis. The observed selectivities for linear and branched Cn+1 and Cn+2 products as well as the linear/branched ratio can be well-explained on the basis of the minimization of steric interactions between 1,2- or 1,3-substituents in the various tantallacyclobutane intermediates or during their formation. Hydrogen plays a specific role in the cleavage of metal alkyls to complete the catalytic cycle. 相似文献
944.
Maji TK Mostafa G Chang HC Kitagawa S 《Chemical communications (Cambridge, England)》2005,(19):2436-2438
Two novel isomorphous porous frameworks of Ln(III), {[Ln2(imidc)2(H2O)3](H2O)}n, [Ln = Gd(III) (1) and Er(III) (2)] have been synthesized hydrothermally using multifunctional 4,5-imidazoledicarboxylic acid (imidc) as a connector; they have a zeolite-like network topology which can provide another form upon dehydration, and exhibit selective adsorption properties for H2O over N2, CO2 and MeOH. 相似文献
945.
946.
947.
Youssef Ahmed O. Khalil Mostafa M.H. Ramadan Ramadan M. Soliman Ahmed A. 《Transition Metal Chemistry》2003,28(3):331-335
M(CO)6 (M = Mo and W) reacts with 2,2-biquinoline (biq) to yield tetracarbonyl derivatives M(CO)4(biq). Crystals suitable for X-ray structure determination of W(CO)4(biq) were isolated from benzene solution. The u.v.–vis. spectra of the complexes exhibited visible transitions due to metal-to-ligand charge-transfers. Electrochemical investigation of the complexes showed some irreversible, reversible and quasi-reversible redox reactions due to tautomeric interconversions through electron transfer. The thermal properties of the complexes were also investigated using the thermogravimetric technique. 相似文献
948.
949.
Mostafa A Abdelkader 《Advances in Applied Mathematics》1983,4(1):39-45
The boundary-value problem ?z″ = (z2 ? t2)z′, ? > 0, z(? 1) = α, z(0) = β, t? [?1, 0], has been shown to have a solution, and moreover, depending on the choice of α and β, multiple solutions to it exist. We consider the more general equation f(z, t)z″ = (zr ? ts)z′ for a particular non-negative function f(z, t), and integrate the equation exactly. Depending on α and β, we find that either there are no solutions, or that only unique solutions exist. The conclusion is that the presence of a continuous locus of singular points, given by zr = ts, does not necessarily produce multiple solutions. 相似文献
950.
Jean-Pierre Fayet Marie-Claire Vertut Alain Fruchier El Mostafa Tjiou Jos Elguero 《Magnetic resonance in chemistry : MRC》1978,11(5):234-238
The carbon-13 chemical shifts and the 1J(CH) coupling constants for 18 azolium salts (di-N-methyl-pyrazolium, -indazolium, -benzimidazolium and -benzotriazolium iodides) have been determined and assigned. The chemical shifts are discussed as a function of substituent effects, positive charge introduction and total electronic density (calculated by the CNDO/2 method). The general problem of correlations between chemical shifts and total charge densities in azoles is discussed. A statistical approach shows that these correlations are of poor quality. 相似文献