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161.
Saida Azzouzi Rachid Jalal Malika El Messaoudi Luis R. Domingo M'hamed Esseffar M. José Aurell 《Journal of Physical Organic Chemistry》2007,20(4):245-254
A novel heterocyclic compound 3‐mesityl‐5‐methyl‐4,5,11,11a‐tetrahydro‐6H‐[1,2,4]oxadiazolo [5,4‐b][1,3,4]benzotriazépin‐6‐one 4 has been synthesised by a 1,3 dipolar cycloaddition (13DC) reaction of 1,3,4‐benzotriazepin‐5‐one 1 with mesitylnitrile oxide 3 . The reaction, beside its synthetic interest, has shown to be completely chemo‐ and regioselective. The structure of the compound was determined by X‐ray crystallography and analysed by spectral methods (NMR and mass spectrometry). The molecular mechanism for the reaction has been studied using quantum mechanical calculations at the B3LYP/6‐31G* theory level. Two mechanisms are possible for the formation of the cycloadduct 4 . The first one involves a 13DC reaction between 1 , as dipolarophile and 3 , as dipole. Analysis of the results indicates that it takes place along asynchronous concerted bond‐formation process with a very low polar character. The regioselectivity obtained from the calculations are in complete agreement with the unique formation of the cycloadduct 4 . The second mechanism is initiated by the nucleophilic attack of the N3 nitrogen of the tautomer form of 2 , to the C5 carbon of the nitrile oxide 3 to yield an amidoxime. However, the large energy involved in this addition prevents this mechanism. The large energy difference between the tautomers 1 and 2 , makes that only the C?N site of benzotriazepin‐5‐one 1 could act as a dipolarophile site. This fact makes the 13DC reaction to be chemoselective. The analysis of global electrophilicity of the reagents allows explaining the low polar character of these 13DC reactions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
162.
If a matrix effect is detected during the validation stage of an analytical method, the standard addition methodology must be applied. To reach a good estimation of the uncertainty associated with the determination, an adequate identification and evaluation of each uncertainty source should be done. As an example to illustrate how to calculate the uncertainty in this case, the simultaneous determination of V(V) and Mo(VI) at trace levels after precolumn chelation and extraction with N-benzoyl-N-phenylhydroxylamine, has been selected. The final results show that the main contributions to the relative overall uncertainty are those closely related with the chemical aspects of the method, i.e. liquid–liquid extraction and standard addition calibration. 相似文献
163.
Roques N Maspoch D Domingo N Ruiz-Molina D Wurst K Tejada J Rovira C Veciana J 《Chemical communications (Cambridge, England)》2005,(38):4801-4803
The synthesis, self assembly and magnetic properties of a polychlorotriphenylmethyl radical, substituted with six meta-carboxylic groups, are reported showing that radical-radical hydrogen bonds in the solid state yield to very weak intermolecular ferromagnetic interactions. 相似文献
164.
Manrubia SC Lázaro E Pérez-Mercader J Escarmís C Domingo E 《Physical review letters》2003,90(18):188102
We explore a mean-field model for the evolution of exponentially growing populations of mutating replicators. Motivated by recent in vitro experiments devised to analyze phenotypic properties of bacterial and viral populations subjected to serial population transfers, we allow our in silico individuals to undergo unrestricted growth before applying bottleneck events. Different dynamical regimes of our model can be mapped to different experimental situations. Numerical and analytical results for fitness distributions calculated at the statistically stationary states of the dynamics compare favorably with available experimental data. Our model and results provide a common framework to better understand populations evolving under different selection pressures. 相似文献
165.
Various experimental dental materials were characterized using chemometric methods. The main aim of the study was to ascertain which composite materials present the best properties for use in restorative dentistry. Bisphenol-alpha-glycidyl methacrylate-based composites containing hydroxyapatite as a filler and a coupling agent were prepared using a photocuring polymerization procedure. Several chemical and mechanical properties of experimental composites were measured and the corresponding data were further studied using principal component analysis and cluster analysis. Results from the characterization allowed the most appropriate materials to be selected. Various composites presented acceptable general properties suggesting their suitability as substitutes for commercial materials in dentistry. 相似文献
166.
K. Gabathuler J. Domingo P. Gram W. Hirt G. Jones P. Schwaller J. Zichy J. Bolger Q. Ingram J. P. Albanese J. Arvieux 《Nuclear Physics A》1980,350(3-4):253-264
The elastic scattering of positive pions by deuterium has been studied at seven energies between 82 MeV and 292 MeV laboratory kinetic energy in the angular range between 30° and 130° (lab). The results are compared to recent relativistic three-body calculations. 相似文献
167.
Cycloprop[b]anthracenes 1, 1a, 1b are prepared in a 3-step synthesis starting from o-di(iodomethyl)benzene. The key step consists of trapping of o-naphthoquinodimethane (9) with 1,2-di- and tetrahalogenocyclopropenes (3, 3a, 4b) . 相似文献
168.
D. Mouhssine A. Nourreddine A. Nachab F. Fernandez C. Domingo H. Muller K. Amgarou A. Pape D. Raiser 《Radiation measurements》2005,40(2-6):612-615
A personal imaging plate (IP) dosimeter is in the process of being developed for neutron fields using the BaFBr:Eu2+ phosphor. A configuration incorporating a polyethylene radiator placed before the IP detector is used to produce protons via (n,p) elastic scattering. For a dosimeter sensitive to thermal neutrons, a Nylon plate ( thick) is placed between the polyethylene (1.2 mm thick) radiator and the IP ( thick sensitive layer) detector to produce protons via the 14N(n,p)14C reaction. Dosimeters having these configurations have been exposed to neutrons from 241Am–Be and 252Cf sources at the Institute for Radioprotection and Nuclear Safety of Cadarache at angles of 0 (normal incidence), 30 and 60 and several dose equivalents. The personal dose equivalent response in terms of Hp(10) is evaluated from the net measured photostimulated luminescence densities (). The calibration factor obtained for estimating the personal dose equivalent with this dosimeter is for 241Am–Be and for 252Cf. 相似文献
169.
Domingo A. Herrero 《Integral Equations and Operator Theory》1978,1(4):580-588
Every compact quasinilpotent Hilbert space operator can be uniformly approximated by operators that are similar to the Volterra operator in L2([0,1],dx). 相似文献
170.
Spence JD Cline ED LLagostera DM O'Toole PS 《Chemical communications (Cambridge, England)》2004,(2):180-181
Condensation of a porphyrin-2,3-dione with a 1,2-diaminoarenediyne affords a [small beta]-extended porphyrinic-enediyne: upon thermal Bergman cyclization the quinoxaline spacer positioned between the macrocycle and the enediyne prevents tandem radical cyclization to a picenoporphyrin. 相似文献