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  • Analytical methods  (16)
  • Polymers  (10)
  • Alkenes
  • Wiley-Blackwell  (30)
  • 1985-1989  (20)
  • 1960-1964  (10)
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  • Wiley-Blackwell  (30)
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  • 1
    ISSN: 0570-0833
    Keywords: Koch carboxylic acid synthesis ; Carboxylic acids ; Alkenes ; Isomerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: When straight-chain mono-olefins, from pentene to decene, are subjected to the Koch carboxylic acid synthesis by the addition of CO and H2O or CH3OH in the presence of strongly acidic catalysts, not only the expected secondary acids, but also mixtures of a specific type of tertiary acids or their methyl esters are formed. When the catalysts contain boron trifluoride, the secondary acids are formed in ratios of isomers which are, within the scope of this investigation, independent of the experimental conditions and which agree well with the values calculated from the isomer equilibria of the corresponding n-olefins. Using concentrated sulfuric acid as catalyst, a larger proportion of tertiary acids is obtained than with BF3-catalysis, and amongst the secondary acids, those isomers predominate in which the COOH group is situated near the centre of the molecule.
    Additional Material: 1 Ill.
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  • 2
    ISSN: 0570-0833
    Keywords: NMR spectroscopy ; Organometallic compounds ; Analytical methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Great advances have been made in the past decade in the field of NMR spectroscopy. Apart from the development of completely new areas of application, such as in solid-state chemistry, in materials science, in physiological chemistry, and in medicine, with the introduction of new pulse spectroscopic methods and the application of high magnetic field strengths important progress has also been made in the traditional field of high-resolution NMR spectroscopy. Thus, among other things, the observation of metal resonances has been facilitated and new areas of application have been opened up in inorganic and organometallic chemistry. In this review, recent detection methods for spin-1/2 and quadrupolar metal nuclei are presented and discussed. The use of metal-NMR spectroscopy with respect to problems of a typical chemical nature, mainly from the field of organometallics, is demonstrated for a number of selected metal nuclei (25Mg, 27Al, 49Ti, 57Fe, 59Co, 61Ni, 91Zr, 103Rh, and 195Pt). Relations found empirically between chemical shifts and coordination number, oxidation number, and electronic configuration of a metal bound in a complex are emphasized. Furthermore, cases in which the chemical shifts of metal nuclei can be interpreted in terms of the energy difference of frontier orbitals are presented. This aspect leads to the establishment of a relationship between chemical reactivity and NMR parameters for a series of related compounds.
    Additional Material: 24 Ill.
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  • 3
    ISSN: 0570-0833
    Keywords: Correlation spectroscopy ; Angular correlation spectroscopy ; Materials science ; Analytical methods ; Spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The study of nuclear quadrupole interactions, i.e. of the strength, symmetry, and orientation of the electric field gradient tensor, yields valuable information on charge density distributions on an atomic scale. Apart from the nowadays “conventional” methods of NMR and Mössbauer spectroscopy there is yet another technique: time-resolved perturbed γ-γ-angular correlation spectroscopy. This technique is very well suited for applications in chemistry (e.g. comparative studies of bond conditions of inorganic complexes in the solid and in solution or in the melt), in molecular biology (e.g. intramolecular dynamics in biomolecules), and in materials science (e.g. investigation of catalyst surfaces) because of, inter alia, the extremely small sample requirements and the temperature independence of the sensitivity. The variation of the electric field gradient tensor (strength, symmetry, possibly orientation) is observed as a function of external parameters or, in the case of reactions, as a function of the degree of reaction. The interpretation of results requires the assignment of observed signals to known species or configurations. In this progress report we review modern areas of application of perturbed angular correlation spectroscopy.
    Additional Material: 16 Ill.
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  • 4
    ISSN: 0570-0833
    Keywords: Surface recognition ; Molecular recognition ; Self-assembly ; Biological membranes ; Membranes ; Polymers ; Micelles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Part and the Whole. The principle of self-organization for the creation of functional units is not an invention of modern natural sciences. It was already a basic idea of the ancient philosophies in Asia and Europe: only the mutuality of the parts creates the whole and its ability to function. Translated into the language of chemistry this means: the self-organization of molecules leads to supramolecular systems and is responsible for their functions. Thermotropic and lyotropic liquid crystals are such functional units, formed by self-organization. As highly oriented systems, they exhibit new properties. The importance of lyotropic liquid crystals for the life sciences has been known for a long time. They are a prerequisite for the development of life and the ability of cells to function. In materials sciences this concept of function through organization led to the development of new liquid-crystalline materials. From the point of view of macromolecular chemistry, this review tries to combine these two different fields and especially hopes to stimulate their interaction and joint treatment. To exemplify this, the molecular architecture of polymeric organized systems will be discussed. Polymeric liquid crystals combine the ability to undergo spontaneous self-organization-typical of liquid-crystalline phases-with the polymer-specific property of stabilizing these ordered states. As new materials, polymeric liquid crystals have already been investigated intensively. As model systems for biomembranes as well as for the simulation of biomembrane processes, they so far have been little discussed. The intention of this review article is to show that polymer science is able to contribute to the simulation of cellular processes such as the stabilization of biomembranes, specific surface recognition, or even the “uncorking” of cells. Polymer science, having an old tradition as an inter-disciplinary field, can no longer restrict itself to common plastics. Attempts to reach new horizons have already begun. The borderland between liquid crystals and cells will certainly play an important role. Basic requirements to work in this frontier area between organic chemistry, membrane biology, life science, and materials science will be the delight in scientific adventures as well as the courage to go ahead. The most important prerequisite will be the willingness to cooperate with disciplines which so far have not really accepted each other. From this point of view, this review does not aim at giving defined answers. It wants instead to encourage the scientific venture: too often we cling to painfully acquired knowledge, fearing adventures.
    Additional Material: 78 Ill.
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  • 5
    ISSN: 0570-0833
    Keywords: Transition metals ; Polymers ; Alkene ligands ; Electrocatalysis ; Complexes ; Alkyne ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An unprecedented series of highly reactive alkene-and diene-complexes of the early transition metals (Groups 3A-5A of the periodic system) have been isolated recently. Diene complexes of this sort (M = Ti, Zr, Hf, Nb, Ta) prefer, besides the (η4-s-cis-diene)metal structure, either a novel bent η4-metallacyclo-3-pentene structure or the unique (η4-s-trans-diene)metal structure. In bis(diene)metal complexes of Nb and Ta the η4-s-cis-dienes assume an unusual exo-endo (supine-prone) geometry. The M—C bonds in these diene-metal complexes generally exhibit highly polarized σ-bonding along with π-bonding character. The complexes therefore undergo a variety of regio- and stereoselective carbometalations with substrates containing C—C, C—O, or C—N multiple bonds. Examples of the products that can be obtained include ketones, vinyl ketones, unsaturated primary, secondary, and tertiary alcohols, as well as diols and unsaturated acids. Mechanistic studies on the stoichiometric and catalytic conversions of unsaturated hydrocarbons provides, inter alia, some insights into the course of polymerization reactions.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0570-0833
    Keywords: Liquid crystals ; Crystalline polymers ; Polymers ; Optoelectronics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The liquid crystalline behavior of low molecular weight compounds has been known for more than a century; synthetic polymers have been manufactured on a large scale for several decades, but just recently it was found possible to produce polymers using the structural principles of liquid crystalline compounds. The resulting materials have, as expected, unusual properties. Numerous applications, not only in opto-electronics, are already anticipated for such materials.
    Additional Material: 9 Ill.
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  • 7
    ISSN: 0570-0833
    Keywords: Chirality ; Optical activity ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Main-chain chirality is the optical activity resulting from the configurational or conformational arrangement in the main chain of a polymer. The chirality of the most important types of structures has been investigated on the basis of systematic considerations of symmetry. This has led to the surprising result that even in polymers derived from 1-substituted or nonsymmetric 1,1-disubstituted olefins (the technologically most important polymers) several types of chiral structures exist, which are expected to result in optical activity if a particular enantiomer is favorably formed. By carrying out an asymmetric cyclopolymerization, it has been possible to obtain certain structural types in the form of optically active copolymers or homopolymers (e.g., copolymers of styrene with methyl methacrylate, or even the homopolymer of styrene). Another new group of optically active polymers consists of the atropisomeric helical polyisocyanides, poly(trityl methacrylates), and polychlorals. Optically active polymers are already used as adsorbents for the chromatographic separation of racemic mixtures. Further applications are likely to emerge.
    Additional Material: 20 Ill.
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  • 8
    ISSN: 0570-0833
    Keywords: Tacticity ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction course and kinetics of interfunctional reactions with polymers are determined by the microtacticity of the polymer chain. Among other things, this is shown by the hydrolysis of ester and amide polymers of different tacticities, and by ring-closure reactions (anhydride formation). The physical and physico-chemical properties are also governed by the tacticity.
    Additional Material: 4 Ill.
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  • 9
    ISSN: 0570-0833
    Keywords: Emulsion polymerization ; Polymerization ; Polymerization ; Alkenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ionizing radiation induces the polymerization of some vinyl monomers in aqueous emulsion with high radiation yields. With identical emulsion compositions, the kinetics of this reaction and the kinetics of emulsion polymerization induced by water-soluble initiators are very similar. The rate of reaction in emulsion polymerization is about one hundred times greater than in bulk polymerization. The initiation of emulsion polymerization by means of ionizing radiation permits uniform “illumination” of the reacting volume, as well as almost any desired variation in the frequency of initiation during the reaction. The sharp decrease in the overall rate of reaction when initiation is interrupted during emulsion polymerization of styrene induced by γ-rays contradicts the earlier concept of sharply separated reaction zones.
    Additional Material: 11 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0570-0833
    Keywords: Oligomers ; Pleionomers ; Polymers ; Fibers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The term “oligomer” is defined, and a survey of methods for the isolation and synthesis of cyclic and linear oligoesters, oligourethanes, oligo(acrylonitriles), and oligoamides is presented. The oligomers serve a valuable function as model substances for the investigation of many properties of the corresponding high polymers. This is shown using several examples (infrared spectroscopy, X-ray spectroscopy, viscosity).
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