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The 1,3-dipolar cycloadditions (13DC) of C-diethoxyphosphoryl-N-methylnitrone and N-(2-fluorophenyl) acrylamide have been studied using density functional theory (DFT) calculations at B3LYP/6-31G(d) level of theory. Our calculations show that this 13DC reaction takes place with complete ortho regioselectivity with endo stereoselectivity, which favours kinetically the formation of the ortho–endo cycloadduct, in agreement with the experimental observations. The inclusion of solvent effects does not modify the gas-phase selectivities but slightly decreases the reactivity of the reagents. Analysis of the bond order and charge transfer at the transition states indicates that this 13DC reaction takes place via a one-step asynchronous mechanism. Analysis of the DFT global reactivity indices and the Parr functions of the reagents allow us to provide an explanation of the regioselectivity of this 13DC reaction. 相似文献
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Salah Chafaa Jean Meullemeestre Marie-Jos Schwing Franois Vierling Volker Bhmer Walter Vogt 《Helvetica chimica acta》1993,76(4):1425-1434
UV/VIS Absorption spectra of nitrosubsituted (o-hydroxyphenyl)methylphosphonic acids (o-(phosphonomethyl)phenols) were measured as a function of pH at 25° in 0.1M NaClo4 solutions. Computational treatment of the whole set of optical density data between 200 and 500 nm resulted in the determination of the dissociation constants of these polyacids and also of the individual electronic spectra of all the species involved in the deprotonation sequence. The spectral behavior gives information on the structure of the anions formed and consequently the order of the subsequent deprotonation steps could be deduced. For the (2-hydroxy-3-nitro(or 5-nitro)phenyl)methylphosphonic acid and the 2-hydroxy-5-nitro-1,3-phenylenebis(methylphosphonic acid), the phenolic proton dissociates in the last step, while, in the case of (2-hydroxy-3,5-dinitrophenyl)methylphosphonic acid, the last dissociating proton comes from a P? OH group. An intermediate situation is found for (3-chloro-2-hydroxy-5-nitrophenyl)methylphosphonic acid. Generally, the deprotonation sequence is governed by intramolecular H-bonds involving the phenolic OH group. 相似文献
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Volker Bhmer Walter Vogt Salah Chafaa Jean Meullemeestre Marie-Jos Schwing Franois Vierling 《Helvetica chimica acta》1993,76(1):139-149
(o-Hydroxyphenyl)methylphosphonic acids are readily obtained from o-(bromomethyl)- or o-(hydroxymethyl)phenols and trialkyl phosphites. Subsequent hydrolysis leads to the corresponding phosphonic acids. For a series of such compounds, the pKa values have been determined by potentiometry. Their dependence on additional substituents in the aromatic ring is discussed in terms of electronic and steric effects. 相似文献
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Nabila Aliouane Salah Chafaa Tahar Douadi Jean‐Jacques Hlesbeux Mustayeen A. Khan Olivier Duval Gilles Bouet 《Heteroatom Chemistry》2010,21(2):51-62
The acido‐basic and the complexation properties of di‐, tri‐, and tetra‐phosphonic acids (H6L1, H8L2, and H10L3) toward Fe(III) and Cu(II) were determined by potentiometric titration in aqueous media at 25.0 ± 0.1°C with constant ionic strength (0.1 M, NaClO4). We have determined six, ten, and eight pKa values for the di, tri, and tetra‐phosphonic acids, respectively. In acidic conditions, e.g., 0 ≤ pH ≤ 5; iron and copper presented a high affinity toward these ligands to give complex species. With the ligand H10L3, [FeL3H7], and [CuL3H6]2− were easily obtained at pH 1.8 and 2.7, respectively. We have determined ten stability constants for the H10L3/Fe system and nine for the H10L3/Cu one; six and four in the cases of H8L2/Fe and H8L2/Cu systems, respectively. Finally, five stability constants were calculated for the H6L1/Fe system and four for the H6L1/Cu one. We have not observed any insoluble species in these complexes in acidic medium as well as in alkaline solutions. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:51–62, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20575 相似文献
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Leila Barama Brahim Bayoud Fouad Chafaa Abdelmalek Khorief Nacereddine Abdelhafid Djerourou 《Structural chemistry》2018,29(6):1709-1721
The selectivity and the nature of the mechanism of the competitive Lewis acid catalysed [4+2]/[2+2] cycloaddition reactions of 1-methyl-1-phenylallene (MPA) with methylacrylate (MA) have been theoretically studied within the Molecular Electron Density Theory using DFT methods at the B3LYP/6-31G(d) theoretical level. DFT reactivity indices indicate that MPA is a strong nucleophile and the LA-MA complex is a strong electrophile. The coordination of LA to MA enhances the reaction rate and increases the asynchronicity of the [4+2] CA reaction, changes the nature of the mechanism from one step to stepwise for the [2+2] CA reaction and increases the polar character of these cycloaddition reactions, which become demands a relatively low activation energy. Analysis of different energy profiles indicates that these competitive LA-catalysed CA reactions favour the formation of a mixture of meta regioisomers in both types of cycloaddition, in which the [4+2] cycloadducts were obtained in majority amount, in agreement with the experiment. Analysis based on Electron Localisation Function topological shows that the favoured [4+2] CA reaction takes place through a non-concerted two-stage one-step mechanism. 相似文献
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Ilhem Kaabi Tahar Douadi Djahida Haffar Salah Chafaa Magali Allain Mustayeen A. Khan Gilles M. Bouet 《Transition Metal Chemistry》2007,32(5):666-673
The crystal structure of a new symmetrical pentadentate N2O3 Schiff base: di[4-(phenylimino)pentan-2-one] ether (H2L) is described. In the solid state, the ligand appears as a keto-imine tautomer, while in DMSO solution, the eneamine form
is observed. This ligand coordinates cobalt(II), nickel(II), copper(II) and cadmium(II). The structures of these new complexes
are described using infrared and electronic spectroscopy, 1H-n.m.r. and d.s.c. The cyclic voltammograms of the ligand and the complexes in DMF are discussed. 相似文献
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Haffar Djahida Douadi Tahar Chafaa Salah Khan Mustayeen A. Bouet Gilles 《Transition Metal Chemistry》2004,29(3):245-250
We have prepared and characterised a new series of metal complexes obtained from 4,4-bis(salicylideneimino)diphenylethane (saldipH2) and cobalt(II), copper(II) and cadmium(II) chlorides. In every case, the coordinating atoms are N and O. However, each compound has its own structure:[Co(saldip)]·2 H2O is monomeric and a mononuclear species, [Cu2(saldip)2(H2O)] is a binuclear complex and finally the cadmium complex is formulated as:[(CdCl2)2(saldipH2)]·CdCl2. An electrochemical study (cyclic voltammetry) indicates that the reduction, as well as the oxidation, of copper in [Cu2(saldip)2(H2O)] proceeds in two steps. For the reduction of the two other complexes, two steps are indicated out: the first is attributed to the reduction of the metal and the second to the reduction of the coordinated ligands. 相似文献
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Nabila Aliouane Jean-Jacques Hélesbeux Tahar Douadi Mustayeen A. Khan Gilles Bouet Salah Chafaa 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):354-364
Abstract New di-, tri-, and tetraphosphonic acids were synthesized starting from four o-hydroxymethyl phenol derivatives and obtained in three steps in good overall yield. The phosphonic acids were isolated and purified using semi-preparative C18 HPLC column. The new compounds were characterized using different spectroscopic methods (1H, 13C, and 31P NMR; ESI MS; and MSn, IR). GRAPHICAL ABSTRACT 相似文献
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