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41.
Trimethylsilyl enol ethers of pentane-2,4-dione and methyl acetoacetate react rapidly with alcohols at room temperature without the need for catalytic assistance to give high isolated yields of trimethylsilyl ethers. 相似文献
42.
Ali Z Al-Rubaie Tarik A Fahad Naji A Aboud 《Journal of organometallic chemistry》2004,689(14):2377-2381
Synthesis of the racemic cyclic telluride, i.e., 2,7-dihydro-1H-dinaphtho-[c,e]tellurepin (1), possessing a C2 axis was based on the reaction of 2,2′-bis(bromomethyl)-1,1′-binaphthalene with potassium tellurocyanate in dry DMSO. Reaction of halogens with 1 gave the diiodo (2), dibromo (3) and dichloro (4) derivatives. Treatment of 1 with iodomethane and iodoethane gave the methyl- and ethyl tellurepinium iodides, 5 and 6, respectively.Compound 1 reduced the carbonyl groups in DDQ and TCQ to hydroxyl groups. Mononuclear palladium(II) complex, [(C22H16Te)2PdCl2], was prepared by reaction of 1 with [PdCl2(NCPh)2].All new compounds were characterized by elemental analysis and spectroscopic techniques. 相似文献
43.
Taha A. Hussien Tarik A. Mohamed Abdelsamed I. Elshamy Mahmoud F. Moustafa Hesham R. El-Seedi Paul W. Pare Mohamed-Elamir F. Hegazy 《Molecules (Basel, Switzerland)》2021,26(7)
Centaurothamnus maximus (family Asteraceae), is a leafy shrub indigenous to the southwestern Arabian Peninsula. With a paucity of phytochemical data on this species, we set out to chemically characterize the plant. From the aerial parts, two newly identified guaianolides were isolated: 3β-hydroxy-4α(acetoxy)-4β(hydroxymethyl)-8α-(4-hydroxy methacrylate)-1αH,5αH, 6αH-gual-10(14),11(13)-dien-6,12-olide (1) and 15-descarboxy picrolide A (2). Seven previously reported compounds were also isolated: 3β, 4α, 8α-trihydroxy-4-(hydroxymethyl)-lαH, 5αH, 6βH, 7αH-guai-10(14),11(13)-dien-6,12-olide (3), chlorohyssopifolin B (4), cynaropikrin (5), hydroxyjanerin (6), chlorojanerin (7), isorhamnetin (8), and quercetagetin-3,6-dimethyl ether-4’-O-β-d-pyranoglucoside (9). Chemical structures were elucidated using spectroscopic techniques, including High Resolution Fast Atom Bombardment Mass Spectrometry (HR-FAB-MS), 1D NMR; 1H, 13C NMR, Distortionless Enhancement by Polarization Transfer (DEPT), and 2D NMR (1H-1H COSY, HMQC, HMBC) analyses. In addition, a biosynthetic pathway for compounds 1–9 is proposed. The chemotaxonomic significance of the reported sesquiterpenoids and flavonoids considering reports from other Centaurea species is examined. 相似文献
44.
A series of new C2-symmetric chiral aza crown ether macrocycles 1–4 have been synthesized from (S)-3-aryloxy-1,2-propanediol and (S)-1,2-propanediol for the enantiomeric recognition of amino acid ester derivatives. These new macrocycles have been shown to be strong complexing agents for primary organic ammonium salts (with K up to 176.93 M?1 and ΔG° up to 12.81 kJ mol?1) by 1H NMR titration. These macrocyclic host exhibited enantioselective bonding toward the d-enantiomer of phenylalanine methyl ester hydrochloride with KD/KL up to 6.87 in CDCl3 with 0.25% CD3OD. 相似文献
45.
Tarik Matrab Bernadette Charleux Eva Cabet-deliry Mohamed M. Chehimi Michel Delamar 《Surface science》2007,601(11):2357-2366
Poly(n-butyl methacrylate), PBMA, chains were grafted by atom transfer radical polymerization (ATRP) from the surface of iron plates using electrochemically attached initiators based on diazonium salts providing an iron/polyphenylene/PBMA structure. This surface-initiated ATRP procedure was controlled by the addition of a small proportion of Cu++ deactivator, but in the absence of any sacrificial initiator. Combined XPS, IR and AFM experiments provide a powerful means for the characterization of the obtained complex iron/polyphenylene/PBMA layered structure. It is possible to measure the thickness of the brominated aryl structure covalently attached to iron. Concerning the PBMA brushes, their presence on the surface was confirmed by IRRAS. The brominated chain end could be traced by XPS testifying for the ATRP character of the polymerization and the thickness of the polymer brushes was determined. The controlled living ATRP character of the polymerization is confirmed through a linear correlation between the thickness of the layer and the degree of polymerization. Measurement of the grafting density of PBMA chains indicates that they are compactly packed and that, approximately, one brominated aryl chain out of two efficiently initiates ATRP. 相似文献
46.
Tarik Ouahrani 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(9):1-11
Local properties of the XSiP2 (X = Be, Mg, Cd, Zn and Hg) compounds are revisited through the partition of static thermodynamic properties under pressure. We pay attention to the metallization that occurs when the investigated compounds undergo a phase transition from chalcopyrite to the NaCl structure. Electron localization function analysis shows that the local valence basin attractors values decrease as a function of pressure. As the pressure increases, the tetragonal distortion (c/a) diminishes while the degree of ionicity enhances. In addition, by means of atom in molecule approach, atomic-like local compressibility and pressures are analyzed. We found that the basins volumes of the investigated compounds in the NaCl phase have lower compressibilities than those in the chalcopyrite phase. According to the predicted core-valence basins, the phosphorus cation is found to be the more affected by the hydrostatic pressure. 相似文献
47.
Tarik Chafik Abdelkader Darir Ouafae Achak Ana P. Carvalho João Pires 《Comptes Rendus Chimie》2012,15(6):474-481
In the present work the adsorption of toluene on microporous activated carbon was chosen as an illustrative example in order to show that different values of the heat effect might be obtained following the procedure used. Values ranging from 85 to 40 KJ/moL were obtained for the isosteric heat of adsorption at different adsorbate loadings using adsorption isotherm data measured under static conditions. However, the application of temperature programmed desorption (TPD) experiments carried out under dynamic conditions yields apparent energy of desorption values that cannot be systematically correlated with the heat of adsorption which is a thermodynamic parameter relevant to the adsorption equilibrium. This issue is of interest because the use of accurate values of the heat of adsorption is important for the correct designing and operating of adsorption facilities. 相似文献
48.
Zine el abidine Bentalha Larabi Moumen Tarik Ouahrani 《Central European Journal of Physics》2014,12(7):511-516
The electron-electron and electron-background interaction energies are calculated analytically for systems with up to N = 6 electrons. The method consists of describing the position vectors of electrons using complex coordinates and all the interaction energies with complex notation, whereby simplifications become possible. As is known, in this type of calculation, complicated expressions involving integrals over many variables are encountered and the trick of using complex coordinates greatly facilitates the exact calculation of various quantities. Contrary to previous analytical calculations, using complex coordinates avoids complicated trigonometric functions from appearing in the integrand, simplifying the exact evaluation of the integrals. The method we have used can be straightforwardly extended to larger systems with N > 6 electrons. 相似文献
49.
Tarik Aougab 《Geometriae Dedicata》2014,172(1):293-302
Let \(\Omega =(\omega _{j})_{j\in I}\) be a maximum size collection of pairwise non-isotopic simple closed curves on the closed, orientable, genus \(g\) surface \(S_{g}\) , such that \(\omega _{i}\) and \(\omega _{j}\) intersect exactly once for \(i\ne j\) . We show that for \(g\ge 3\) , there exists atleast two such collections up to the action of the mapping class group, answering a question posed by Malestein, Rivin and Theran. As a consequence, we show that the automorphism group of the systole graph for \(S_{g}, g\ge 3\) (whose vertices are isotopy classes of simple closed curves, and whose edges correspond to pairs of curve intersecting once) does not act transitively on maximal complete subgraphs. 相似文献
50.
Félix G Abdul-Kader K Mahfoud T Gural'skiy IA Nicolazzi W Salmon L Molnár G Bousseksou A 《Journal of the American Chemical Society》2011,133(39):15342-15345
Nano-objects and thin films displaying molecular spin-crossover phenomena have recently attracted much attention. However, the investigation of spin crossover at reduced sizes is still a big challenge. Here we demonstrate that surface plasmon polariton waves propagating along the interface between a metal and a dielectric layer can be used to detect the spin-state changes in the latter with high sensitivity, even at the nanometer scale. 相似文献