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  • Chemistry  (24)
  • Life and Medical Sciences  (3)
  • Quantum optics, physics of lasers, nonlinear optics, classical optics
  • 1985-1989  (27)
  • 1989  (27)
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Keywords
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  • 1985-1989  (27)
Year
  • 1
    Electronic Resource
    Electronic Resource
    On the Tautomerism of 2-Phenacyl-4-pyrimidinones and Related Compounds (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 919-924 
    Details
    ISSN: 0009-2940
    Keywords: Pyrimidinones ; Tautomerism ; AM1 calculations ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zur Tautomerie von 2-Phenacyl-4-pyrimidinonen und verwandten Verbindungen3-Methyl-2-phenacyl-4-pyrimidinone 1, 2 werden durch Sulfidkontraktion synthetisiert. Aufgrund der NMR-Daten existieren die Verbindungen ausschließlich in der Benzoylmethylen-Form, sowohl in Lösung als auch als Festkörper. Diese Ergebnisse werden durch AM1-Berechnungen für die Stammverbindung bestätigt. Die Untersuchung des Tautomeren-Gleichgewichts mittels dieser semiempirischen Methode wurde auf andere Fälle von Enaminoketon/Enolimin-Tautomerie erweitert.
    Notes: 3-Methyl-2-phenacyl-4-pyrimidinones 1, 2 have been synthesized using the sulfide contraction. According to the NMR data, the compounds 1, 2 exist exclusively as the benzoylmethylene tautomers a both in solution and in the solid state. AM1 calculations of the parent system are in agreement with the experimental observations. The study of the tautomeric equilibrium by this semiempirical method has been extended to other cases of enamino-ketone/enolimine tautomerism.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891220521
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  • 2
    Electronic Resource
    Electronic Resource
    Stereospecific functionalization of poly(vinyl chloride)Dedicated to Prof. P. Rempp on the occasion of his 60th birthday (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 223-230 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The substitution reaction of PVC with sodium dimethyldithiocarbamate (NaDC) and sodium azide (NaN3) was performed in cyclohexanone and dimethylformamide at various temperatures. The degree of compositional heterogeneity was estimated and found to be important up to conversions of about 0,5%, but to vanish afterwards. The evolution of unreacted iso, hetero and syndiotactic triads was measured by 13C NMR spectroscopy. For conversions of at least up to 12%, the content of both the isotactic and heterotactic triads was found to decrease, relative to the syndiotactic ones, but at different relative rates depending on the nucleophile. From these results, together with the kinetic ones, it is concluded that the reaction proceeds by a stereoselective mechanism. The results are discussed on the basis of a hypothesis concerning the role of the local triad conformations in PVC that contain the TT isotactic diad conformation. The results enable the selective substitution of PVC with NaDC and NaN3, which may be used as a useful tool to prepare specific graft copolymers based on PVC.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900201
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  • 3
    Electronic Resource
    Electronic Resource
    Tacticity and dielectric relaxation around the glass transition of poly(vinyl chloride). A thermally stimulated depolarization currents (TSDC) study (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 893-905 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermally stimulated depolarization currents (TSDC) technique has been used to study molecular motions around the glass transition in three different samples of poly(vinyl chloride) (PVC) varying in the contents of isotactic triads. The α-relaxation mode associated with cooperative molecular motions taking part in glass transition appears to be strongly dependent on tacticity. A secondary relaxation mode α′, different from the β-relaxation, has been detected just below the α-relaxation and at temperatures depending on the content of isotactic triads. Above the glass transition temperature the TSDC curves show a ρ-peak corresponding to the motion of free charges in the material. This process does not seem to be affected by tacticity. The results suggest that specific conformations of isotactic triads play an important role in the motion of chain segments in the polymer.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900422
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  • 4
    Electronic Resource
    Electronic Resource
    Properties of polyacetylene obtained with (η-Cp)2Ti(PMe3)2 (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 1309-1317 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Acetylene was polymerized by (η-Cp)2Ti(PMe3)2 at room temperature to give predominantly trans-polyacetylene. All properties are within the ranges reported for polyacetylene produced with Ti(OBu)4/AlEt3 as catalyst.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900611
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  • 5
    Electronic Resource
    Electronic Resource
    Structural analysis of poly(3-alkylthiophene)s (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 3105-3116 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(3-hexylthiophene) (PT6), poly(3-octylthiophene) (PT8), poly(3-decylthiophene) (PT10) and poly(3-dodecylthiophene) (PT12) were synthesized by electrochemical and chemical polymerization. Investigation of these polymers by means of gel permeation chromatography indicates that the polymers prepared from the different monomers under similar conditions do not differ substantially considering molecular weight and molecular weight distribution. Bimodal distributions were found for electropolymerized polymers, and with increasing polymerization time, the high-molecular-weight and probably highly branched fraction increased relatively to the low-molecular-weight fraction. The microstructure of the polymers was investigated by nuclear magnetic resonance, and it has been found that the polymers exhibit more types of structural units than expected from a simple coupling of adjacent thiophene moieties in 2,5′-positions. Chemical oxidation with iron trichloride in chloroform gave soluble, high-molecular-weight poly(3-alkyl-thiophene)s with a rather low amount of irregular couplings, and these more regular polymers exhibited a higher degree of crytallinity. Room temperature conductivities of the oxidized polymers were between 0,1 and 30 S/cm depending on the polymerization conditions, but these values were rather independent of the length of the alkyl substituent.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021901208
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  • 6
    Electronic Resource
    Electronic Resource
    Tacticity and dielectric relaxation around the glass transition of poly(vinyl chloride), a dynamic-dielectric study (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 3257-3267 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Molecular motions of poly(vinyl chloride) (PVC) in the glass transition range were studied by means of dielectric spectroscopy. The measurements were carried out with three different PVC samples obtained at different polymerization temperatures (0, 60 and 90°C) showing strong variations in their contents of syndiotactic, heterotactic and isotactic triads. The results show that all parameters (relaxation strength, temperature of the maxima of loss curves, evolution of the shift factors, master curves) characterizing the dielectric α-relaxation in the liquid state of PVC are strongly affected by the tacticity. These facts are interpreted in terms of the role of specific local conformations in the motion of chain segments in the polymer molecules. These conclusions are in agreement with those outlined from the results previously obtained on PVC for the molecular motions in the glassy state just below the glass transition temperature.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021901223
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  • 7
    Electronic Resource
    Electronic Resource
    Influence of the structure on the photodegradation of poly(vinyl chloride), 3.Part 2: cf.5. Dependance of the quantum yield of dehydrochlorination on the isotactic content (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 477-485 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photodehydrochlorination of four poly(vinyl chloride) (PVC) samples of different tacticities, as studied previously, was compared with that of a PVC sample after being modified to various degrees by nucleophilic substitution with sodium benzenethiolate (NaBT). In order to separate the influence of substituted structures from that of the chromophoric group grafted onto the polymer, a series of PVC mixtures with sec-butyl phenyl sulfide (BPT), of compositions similar to those of modified polymers was also studied. The evolution of HCl was found to be a linear function of the absorbed dose in all cases. The quantum yield of dehydrochlorination, ΦHCl, as obtained from the slopes, appeared to decrease with the isotactic content. The results suggest specific isotactic triads to be markedly reponsible for the photodehydrochlorination, which would account for a mechanism based on the occurrence of chlorines of low dissociation energy at such triads.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900304
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  • 8
    Electronic Resource
    Electronic Resource
    Microscopic study of the pyloric caeca of the starfish Marthasterias glacialis (Echinodermata): Finding of endocrine cells (1989)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 202 (1989), S. 151-164 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The ultrastructure of five epithelial cellular types is described. (1) Absorptive-storing cells possess a striated border and accumulate lipids and glycogen. They also contain an apical multivesicular complex and numerous membrane-bound PAS-positive granules of unknown significance. (2) Zymogenic cells contain numerous, large secretory granules. These cells also possess microvilli and accumulate lipid droplets. (3) Current-producing cells contain bundles of thick and thin myofilaments and extend from the basal lamina to the lumen. (4) Mucous cells display the characteristic features of such secretory cells. (5) In addition to these four cellular types, already observed under the light microscope by other authors, endocrine cells have also been identified by both light and electron microscope. They contain variable amounts of secretory granules of diverse sizes and electron densities. Immunocytochemical studies reveal the presence of cells immunoreactive to somatostatin, glucagon, and pancreatic polypeptide. Intraepithelial nerve fibers in contact with endocrine cells are also present. As far as we know, this appears to be the first description of enteroendocrine cells in the phylum Echinodermata.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1052020203
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  • 9
    Electronic Resource
    Electronic Resource
    Acetylene-norbornene copolymers (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 3937-3949 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metathesis ring opening polymerization has been used to copolymerize norbornene and 7,8-bis(trifluoromethyl)tricyclo[4,2,2,02,5]deca-3,7,9-triene. Subsequent thermal elimination of the precursor copolymers yielded acetylene-norbornene copolymers. The undoped copolymers were found to have electrical conductivity, spin concentration, and EPR linewidths which vary with composition. The location of the trans-C—H out-of-plane vibration, however, was invariant at 1010cm-1 indicating that conjugation length of n 〉 4 are present even at 40% acetylene content in the copolymer. The copolymers containing 79 mol % of acetylene units attained a doped conductivity of 0.02 S/cm with a dopant concentration of 6 mol % of I3- per sp2 carbon.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1989.080271206
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  • 10
    Electronic Resource
    Electronic Resource
    Single-column ion chromatography for the determination of chloride, sulfate, and nitrate in water (1989)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 12 (1989), S. 568-569 
    Details
    ISSN: 0935-6304
    Keywords: HPLC-IC ; Inorganic anions ; Water analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240120822
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