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  • Electrocyclic reactions  (1)
  • Electrophilic addition  (1)
  • Hydrogen production  (1)
  • 1
    Electronic Resource
    Electronic Resource
    4,5-Diazafluorenylidene: Preparation, Reactivity, Multiplicity, and Selectivity StudiesDedicated to Professor H. D. Scharf on the occasion of his 65th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1611-1618 
    Details
    ISSN: 0947-3440
    Keywords: Carbenes ; Cycloadditions ; Diazo compounds ; Styrene ; Electrophilic addition ; Nitrogen heterocycles ; Photolysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemistry of 4,5-diazafluorenylidene (3), generated from the diazo compound 3a by photolysis, has been studied with regard to reactivity, multiplicity and selectivity. Reaction of 3 in 2,3-dimethylbutene gave exclusively ketazine 24. The [1 + 2] cycloaddition with styrenes 5-11 afforded cyclopropanes 16-23 in 25-54% yields and 24 as a side product. In these reactions no diazirine intermediate was involved. Irradiation of 3a in methanol afforded the ether 26 (25% yield). The stereoselectivity of 3 was studied by its addition to (E)- and (Z)-β-methylstyrene. A mixture of the (E)- and (Z)-cyclopropanes 22 and 23, respectively, was detected. Thus for 3, triplet multiplicity was concluded. The results of competition experiments with singlet/triplet scavengers (methanol/dimethylbutadiene) demonstrated that an equilibrium between singlet and triplet manifold of 3 exists at room temperature. Selectivity studies with carbene 3 were carried out by evaluating the competition experiments of the cycloaddition of 3 with differently substituted styrenes. A plot of the krel values from the competition studies versus Hammett σ constants gave ρ = -0.65 indicating that carbene 3 reacts as an electrophile.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970745
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  • 2
    Electronic Resource
    Electronic Resource
    Modellsysteme zur artifiziellen Photosynthese - Synthese und Elektronentransferstudien neuartiger Sensibilisator-Relais-EinheitenHerrn Prof. Dr. C. W. Jefford zum 65. Geburtstag gewidmet. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 407-413 
    Details
    ISSN: 0947-3440
    Keywords: Artificial photosynthesis ; Electron transfer ; Sensitizer-relais assemblies ; Photophysical properties ; Hydrogen production ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modell Systems for an Artificial Photosynthesis - Synthesis and Electron Transfer Studies of Novel Sensitizer-Relais AssembliesSyntheses and determination of electron transfer rates between sensitizers and electron acceptors for a novel class of bis(4,4′-dimethyl-2,2′-bipyridine)[4,4′-bis(alkoxymethyl)-2,2′-bipyridin]ruthenium(II) complexes 6-8 are described. We report on the formation of supramolecular complexes between the dialkoxybenzene-tethered bisheteroleptic Ru(II)-bipyridine complexes 5, 8 and 1,1′-dimethyl-4,4′-bypiridinium (MV2+) and cyclo-[bis(1,1′-p-xylylene-4,4′-bipyridinium)] (BXV4+), respectively. Evidence for the formation of supramolecular sensitizer-relais assemblies is taken from the viologen radical and hydrogen production rates in sacrificial model systems for artificial photosynthesis.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950249
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  • 3
    Electronic Resource
    Electronic Resource
    Perspectives in Photochromism: A Novel System Based on the 1,5-Electrocyclization of Heteroanalogous Pentadienyl AnionsDedicated to Professor Emanuel Vogel and Professor Klaus Hafner on the occasion of their 60th birthdays (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 413-431 
    Details
    ISSN: 0570-0833
    Keywords: Photochromism ; Electrocyclic reactions ; Cyclization ; Pentadienyl anions ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular process whereby light induces color changes in certain substances, namely photochromism, is currently a topic of active research. Many reactions - mainly monomolecular - have been reexamined in greater detail from the standpoint of photochromism. Those found to be especially suitable for such studies include cis-trans isomerizations, pericyclic reactions, tautomerizations and dissociations. The most important in this group are undoubtedly the electrocyclization reactions. In this paper we present spiro[fluorene-9,1′-[1,8a]-dihydroindolizine] and its bis- and tris-aza analogues as examples of a promising new system with a wide range of variability. Not only the classical uses, but also those in new fields such as frequency doubling of laser radiation, holography or molecular microcircuit chips can now be considered.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198904131
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