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  • 1
    Electronic Resource
    Electronic Resource
    Stereocontrolled Alkylation of Chiral Pyridinium Salt Toward a Short Enantioselective Access to 2-Alkyl- and 2,6-Dialkyl-1,2,5,6-Tetrahydropyridines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1391-1399 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Alkylations ; Asymmetric synthesis ; Grignard reactions ; Nitrogen heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Treatment of salts 1a-b with Grignard reagents gives, after reduction of the resulting unstable dihydropyridines 7, the tetrahydropyridines 8a-c, with modest selectivities but in very few steps and under practical conditions. Higher stereo- and regioselectivities are obtained with salt 1c which gives the tetrahydropyridines 15a-e. In addition, the dihydropyridine intermediates 11b cyclize to give the new oxazolidine derivatives 12a-e, which turn out to be good precursors of the 2,6-trans-disubstituted tetrahydropyridines 21a-e. Selective syntheses of (-)-lupetidin, (+)-solenopsin, and indolizidines (-)-5 and (-)-6 are presented as representative examples of applications.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical characterization of H2 adsorption on AuPt clusters (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 67 (1998), S. 399-409 
    Details
    ISSN: 0020-7608
    Keywords: Au ; Pt ; H2 adsorption ; AuPt clusters ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Linear and triangular AuPtn cluster reactions with H2 are studied theoretically, using ab initio multiconfiguration self-consistent field (MC-SCF) calculations, followed by extensive multireference configuration interaction (MR-CI) variational and perturbative. Both the linear dimer and the triangular trimers capture the hydrogen molecule by the Pt cluster side and by the Au cluster side. Gold has an electronic effect on the Pt activity, more important than a geometrical one, poisoning the Pt activity to dissociate H2 and lowering the adsorption heats. This effect is stronger in the AuPt dimer, where the H2 capture occurs only at the molecular level, without showing hydrogen bond dissociation. The trimers look more active, relaxing the H(SINGLE BOND)H bond until breakage. No activation barriers are observed in all the cases considered. The hydrogen molecule is not able to cross the clusters due to the large barriers present.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 399-409, 1998
    Additional Material: 2 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical studies on hydrogen activation by iridium dimers (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1029-1035 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The basic and fundamental mechanisms governing the catalytic reaction of small iridium clusters with H2 are presented here with the purpose to determine its behavior in hydrogenation reactions. The iridium dimer/s lowest states in interaction with H2 potential energy surface were obtained using ab initio multiconfigurational self-consistent-field calculations (MC-SCF), with relativististic pseudopotentials. The electronic correlation contribution was included by configurations interaction (CI) calculations, which considered a variational part plus a second-order perturbative part. The Ir2+H2 reactions were developed in the C2v symmetry. The Ir2's five lowest electronic states were determined, 5Πg, 3Πg, 1Σg+, 3Σu+, and 5Σg, and studied when reacted with H2. It was found that the iridium dimer, in these five states, might capture and break the H—H bond, spontaneously in certain cases and after surmounting activation barriers in other cases.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1029-1035, 1998
    Additional Material: 6 Tab.
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  • 4
    Electronic Resource
    Electronic Resource
    Viscoelastic properties of acrylonitrile-butadiene-styrene (ABS) polymers in the molten state (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1394-1406 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The viscoelastic behavior of acrylonitrile-butadiene-styrene (ABS) terpolymers is studied in the molten state. First, the behavior of the styrene-acrylonitrile (SAN) matrix is determined. Then, the effect of the degree of grafting on ABS rheological properties is emphasized. A critical degree of grafting (DGc), corresponding to a minimum of the viscoelastic functions in the low frequency region, is determined. It defines a critical thickness of the grafted layer, and is related to the conformation of the grafted chains at the surface of the rubber particle. The DGc affects the morphology of the ABS and also affects the appearance of a secondary plateau at low frequencies. The effects of the rubber particles, of the grafted chains, and of the morphology on the appearance of the secondary plateau at low frequencies are clearly dissociated.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760351711
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis of the evolution of microcreep during physical aging and mechanical deformation in poly(methyl methacrylate) using a microstructural model (1984)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 921-929 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The evolution of poly(methyl methacrylate) (PMMA) during physical aging at 90°C is followed by torsional microcreep tests. On the aged specimen a longitudinal stress is applied which induces a strain of 5 percent after 30 days of creep. The torsional microcreep tests are performed during the longitudinal creep in order to compare the structure evolution of PMMA caused by straining with its evolution measured during aging. The microcreep, for the first 800s, follows a reversible logarithmic law. In this stage the mobile defects achieve their activated form which is perfectly reversible when unloaded. The physical aging reduces this logarithmic part of microcreep. This is due to the decrease of either the number or the volume of the mobile defects. Beyond a critical elongation ∊ = 1 percent, the longitudinal straining has just the opposite influence, i.e., the logarithmic part of microcreep increases. This critical elongation ∊ = 1 percent corresponds to the beginning of the steady state longitudinal creep. The transient that precedes this steady state has no detectable influence on the structure of the specimen.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760241112
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  • 6
    Electronic Resource
    Electronic Resource
    A comparison of the combination of fast-atom bombardment with tandem mass spectrometry and of gas chromatography with mass spectrometry in the analysis of a mixture of kaempferol, kaempferide, luteolin and oleouropein (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 427-436 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Two different approaches, i.e. fast-atom bombardment tandem mass spectrometry and gas chromatography combined with mass spectrometry (GC/MS) have been employed for the characterization of a mixture of biologically relevant polyphenols (kaempferide, kaempferol, luteolin and oleouropein). The best results have been achieved by the first approach which allows an easy structural identification of the different compounds, also in the presence of isomers. GC/MS of the trimethylsilyl derivatives leads to a complex chromatogram due to the presence of derivatives exhibiting a different level of silylation; the only species related to oleouropein are due to pyrolysis products (silylated fragments of sugars) and there is no evidence for the related silylated aglycone.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290090512
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  • 7
    Electronic Resource
    Electronic Resource
    Criteria for the Stability of Miscible Displacement through Porous ColumnsPaper presented by M. Quintard at the annual meeting of German Chemical Engineers, Strasbourg, Sept. 17-19, 1986. (1987)
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 59 (1987), S. 354-355 
    Details
    ISSN: 0009-286X
    Keywords: Porous medium ; Miscible displacement ; Stability criteria ; Energy method ; Linearized amplitude equation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cite.330590424
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  • 8
    Electronic Resource
    Electronic Resource
    Etude par Microscopie Raman de la Couche Liquide Situee au Contact d'un Cristal de NaNO3 en Cours de Dissolution dans sa Solution Mère (1989)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 20 (1989), S. 227-232 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The efficiency of Raman microscopy coupled with multichannel acquisition of data was tested for studying the dissolution layer of a mineral salt in its undersaturated mother solution. Experimental work was carried out on sodium nitrate solutions at concentrations ranging between 0.05 and 7.8 M. At lower concentrations the existence of three main species, free aquated ions, solvent-separated ion pairs and contact ion pairs, was confirmed spectroscopically, in addition to a small amount of aggregates (NO3- · Na+)n which occur only at high concentrations ([NO3-]〉2 M). Gaussian-Lorentzian parameters of each ν1(A′1) band characteristic of such individual species were calculated and were found to vary considerably depending on whether the Raman spectra were recorded with a standard scanning system or with a multichannel detector. When the laser beam was focused at the interface between a dissolving NaNO3 crystal and the sodium nitrate solution ([NO3-]=4.68 M), the micro-Raman spectra showed that the concentration of aggregates was considerably increased compared with that determined in the same way in the bulk of the nitrate solution. The technique used to obtain reliable spectra of the dissolution layer is discussed in detail.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250200406
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  • 9
    Electronic Resource
    Electronic Resource
    Raman microspectrometric study of the dissolution layer of M(NO3)2·nH2O crystals (M = Mg, Ca, Zn and Cd) in their undersaturated aqueous solutions (1991)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 22 (1991), S. 169-176 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The composition of the dissolution layer of certain divalent metal nitrates crystals such as Mg(NO3)2, Ca(NO3)2, Zn(NO3)2 and Cd(NO3)2 in their respective undersaturated solutions was studied by Raman microspectrometry using multi-channel acquisition of data. A preliminary examination of homogeneous saturated and 20% undersaturated solutions of every solute considered confirmed the existence of individual Raman bands which could be assigned to different solvated species, namely free aquated ions, solvent-separated ion pairs and contact ion pairs. Some spectral differences were noted between the four cations involved. With Ca2+, Zn2+ and Cd2+ a weak band, assigned to ion aggregates, was also identified. Micro-Raman spectra of dissolution layers recorded at several steps of the crystal dissolution showed a considerable increase in the proportions of aggregates or contact ion pairs, depending on the type of solute examined. Sharp differences between the dissolution layer composition for Group IA, IIA and IIB metal nitrates were observed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250220306
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  • 10
    Electronic Resource
    Electronic Resource
    Etude par Microscopie Raman de la Couche Liquide Située au Contact d'un Cristal en Cours de Dissolution dans sa Solution Mère: Systèmes LiNO3—H2O et KNO3—H2O (1989)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 20 (1989), S. 707-715 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The composition of the dissolution layer of LiNO3 and KNO3 crystals in their respective unsaturated mother liquors was studied by Raman microscopy coupled with a multi-channel acquisition of data. Preliminary examination of homogenous solutions at various concentrations of LiNO3 and KNO3 revealed the existence of individual Raman bands assigned to different solvated species, namely free aquated ions, solvent-separated ion pairs and/or contact ion pairs. Weak bands due to a small amount of aggregates (LiNO3)n or (KNO3)n were also identified. Spectral parameters of each individual band were calculated. Raman spectra of dissolution layers recorded at different steps of the crystal dissolution revealed considerable reinforcement of aggregates and contact ion pair concentrations compared with that existing in the bulk of the unsaturated mother liquors. The aggregate concentration in the dissolution layer was found to be even higher than that calculated for the corresponding saturated solution. The behaviours of LiNO3 and KNO3 were shown to differ considerably.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250201102
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