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  • 1
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High resolution 1H NMR is applied to the study of hydrolysis and equilibria in the complex system of γ-[1-methyl-5-bis(β-chloroethyl)amino-2-benzimidazolyl]butyric acid and D2O. Kinetic data for the individual hydrolytic steps are obtained for the first time. The hydrolytic reactions are pseudo first order. The differences in the activation energies of the two hydrolysis steps are accounted for by different intermediates. Furthermore, equilibrium constants for the deuteration of the N mustard group in the individual products are quantitatively estimated. They show an increase of the basicity of N mustard with hydrolysis. The applicability of the 1H NMR method is restricted to a pD range of 0.5-4.
    Additional Material: 6 Ill.
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  • 2
    ISSN: 0749-1581
    Keywords: Mercury chlorides ; 199Hg chemical shifts ; Chemical exchange ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 119Hg NMR chemical shifts of the stable mercury species HgCln2 - n with n = 0-4 were determined by a least-squares algorithm from 199Hg chemical shifts measured in 50 mM aqueous mercury solution as a function of the chlorine concentration at 25°C. The concentrations of the corresponding mercury species in the solutions necessary in this special procedures were calculated by using published equilibrium constants. The results relative to dimethyl-mercury are -2256 ppm (Hg2+), -1897 ppm (HgCl+), -1560 ppm (HgCl2), -1436 ppm (HgCl3-) and -1152 ppm (HgCl42-) with maximum errors of ±5 ppm.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 1435-1536
    Keywords: Microemulsions ; diffusion ; NMR ; QELS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Diffusion studies were performed with various methods to obtain some insight into the structure and the dynamical processes of three and four component microemulsions containing p-nonylphenol ethylene oxide adducts which were mixtures of highly branched p-nonyl isomers with well defined distributions of the ethylene oxide chain length. Diffusion coefficients were determined by pulsed field gradient and pulsed field gradient Fourier transform1 H NMR as well as by quasi-elastic light scattering. The combined application of pulsed field gradient NMR and quasi-elastic light scattering gives information about the critical behaviour of the systems whereas pulsed field gradient Fourier transform NMR allows the determination of the diffusion coefficients of the individual constituents. The results suggest that the very complex three and four component microemulsions studied undergo critical concentration fluctuations in a large temperature region from about 15 °C below the lower critical solution temperatures. The deduced critical exponents are in good agreement with theoretical predictions. The aggregates in the three and four component microemulsions show differences in the self diffusion behaviour of their constituents.
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  • 4
    ISSN: 1435-1536
    Keywords: Monte Carlo method ; oriented branched chain ; order parameter ; molecular shape
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The conformational behaviour of phosphonic acid dialkyl ester (PAE) molecules in a uniaxial hydrophobic environment was studied using the Monte Carlo method with the well-known Metropolis algorithm. The influence of the surrounding molecules on ordering processes of the intrinsic PAE molecules was taken into account by a molecular field. The intramolecular energy was calculated using 6–12 atom-atom and torsion potential functions. Conformations were analysed using torsion angle distributions, segment and bond order parameters. The order parameters of the C-H bonds are compared with experimental results of2H NMR. Further a general method of determining the effective shape of a molecule is presented. The shape is defined by probability distribution for finding atomic coordinates within volume elements during a Monte Carlo run. Thus the asymmetry of a molecule can be visualized. PAE molecules studied show a positive asymmetry in all cases.
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  • 5
    ISSN: 1435-1536
    Keywords: Key words Metal silicate hydrate layers ; infrared linear dichroism ; order parameter ; orthorhombic subcell ; tilt angle ; trimethylammonium group
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Microcrystals of the metal silicate hydrate ilerite orient macroscopically on the surface of a ATR-crystals and thus, are accessible for infrared linear dichroism measurements. We present first results which indicate that the alkyl chain packing and the orientation of the polar group of dodecyltrimethylammoniumbromide (DTAB) intercalated between silicate layers can be determined in terms of infrared order parameters. The properties of DTAB can be modulated by the relative humidity of the surrounding atmosphere and by temperature. Upon heating DTAB undergoes a phase transition from a paraffin-like solid to a fluid phase. The former is characterized by the orthorhombic perpendicular packing of the frozen alkyl chains with tilted long axes. The interactions between the ionic groups of the surfactant and that of the host matrix stabilize the lamellar arrangement of DTAB in the crystalline and in the fluid phases.
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  • 6
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The stability constants for metal and proton chelates of some β-thioxoketones were determined potentiometrically in dioxane-water mixture, and the influence of substituents on chelate stability was studied for zinc compounds as a model. Additional information about the stability of the proton chelates could be received by NMR spectroscopic work from the chemical shifts of methine and hydroxyl protons. The dependence of complex stability on the nature of central ions is discussed by means of stability data for metal chelates of thiodibenzoyl-methane.
    Notes: Die Stabilitätskonstanten der Metall- und Protonenchelate einer Reihe von β-Thioxoketonen wurden auf potentiometrischem Wege in Dioxan-Wasser-Mischung bestimmt und am Beispiel der Zinkchelate der Einfluß der Substituenten auf die Chelatstabilität studiert. Weitere Aussagen über die Stabilität der Protonenchelate konnten durch NMR-spektroskopische Untersuchungen aus den chemischen Verschiebungen für Methin- und Hydroxylprotonen erhalten werden. Die Abhängigkeit der Komplexstabilität vom Charakter des Zentralatoms wurde an Hand von Stabilitätskonstanten für Metallchelate des Thiodibenzoylmethans diskutiert.
    Additional Material: 2 Ill.
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  • 7
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acetylthioacetamides exist as different keto and enol isomers in chloroform solutions. The keto form with intramolecular hydrogen bonding between the NH and the carbonyl group is the dominant keto isomer. On the other hand the enol forms with intramolecular hydrogen bonding between the OH and the thioketo group are the dominant enol isomers in the temperature range 60°C to -60°C. The thermodynamic data of the keto-enol equilibria were obtained by measuring the intensities of appropriate high resolution proton signals as a function of temperature. At low temperatures all lines characteristic of the enol forms are doubled in the N-phenyl-substituted derivatives because the rotation of the NH—C6H5 group around the C—N bond becomes slow and the chemical shifts characteristic of the E and Z isomers are different. We estimated approximate thermodynamic data of the E/Z equilibrium in some of the compounds. The changes of the line shape as well as the chemical shifts as a function of temperature indicate the presence of various additional exchange processes. In order to obtain further information we performed curve fittings of the chemical shifts of one acetylthioacetanilide and of a series of monothio-β-diketones (studied in another paper) assuming a fast two site exchange process. On the basis of the results obtained a reaction scheme for N-substituted acylthioacetanilides in solution is proposed.
    Additional Material: 8 Ill.
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  • 8
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die MICHAEL-Addition von Methylvinylketon an 1-Acetyl-2-benzyl-3-carbomethoxy-4-piperidon verläuft vollständig stereoselektiv und liefert in zwei Reaktionsstufen praktisch ausschließlich eines von vier möglichen Enantiomerenpaaren des 1-Benzyl-2-acetyl-6-keto-9-carbomethoxy-10-hydroxy-decahydroisochinolins (IIIa), wie aus der quantitativ gelungenen Trennung der Säure (IIIb) in die optischen Antipoden hervorgeht. Aus der Rotationsdispersion ergibt sich eine cis-Verknüpfung der beiden Ringe, die außerdem chemisch bewiesen wird.Die Reduktion der 6-Ketogruppe nach MEERWEIN-PONNDORF-VERLEY bzw. durch katalytische Hydrierung an RANEY-Nickel führt überwiegend zum entsprechenden axialen Alkohol, während die Reduktion mit Natriumborhydrid ein Gemisch von äquatorialem und axialem Alkohol (etwa 2:1) liefert. Durch Überführung des äquatorialen Alkohols in das Lacton wird bewiesen, daß von den beiden denkbaren cis-Konformationen diejenige mit (in bezug auf den Cyclohexanring) axialer 9-Carboxylgruppe entstanden ist. Das steht auch in Übereinstimmung mit den Verseifungsgeschwindigkeiten von IIIa und anderen Estern dieses Systems und den Ergebnissen der NMR-Spektroskopie.Die Konformation der Benzylgruppe ließ sich mit Hilfe der IR- und der NMR-Spektroskopie ermitteln.Die Ergebnisse erlauben es, die absolute Konfiguration der Verbindung IIIa festzulegen.Die Gründe für den gefundenen sterischen Verlauf der MICHAEL-Addition werden erörtert und einige allgemeinere Folgerungen daraus abgeleitet.
    Additional Material: 1 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Friedel-Crafts-Acylation of 8-Hydroxyquinoline
    Additional Material: 1 Ill.
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  • 10
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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