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  • 1
    Electronic Resource
    Electronic Resource
    Über sterisch gehinderte freie Radikale, XV. Das erste unsymmetrische Dimere aus zwei stabilen Radikalen: 3-(tert-Butylphenylmethylen)-6-(triphenylmethyl)-1,4-cyclohexadien aus tert-Butyldiphenylmethyl und Triphenylmethyl (1986)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 119 (1986), S. 2006-2012 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Sterically Hindered Free Radicals, XV. The First Unsymmetrical Dimer from Two Different Stable Radicals: 3-(tert-Butylphenylmethylene)-6-(triphenylmethyl)-1,4-cyclohexadiene from tert-Butyldiphenylmethyl and TriphenylmethylThe quinonoid title compound 6 is formed in an equilibrium to 95% and can be isolated, when the two title radicals 1 and 3 are generated in solution. The reason for this is the sterically less strained position of the bulky tBu group at the sp2-C atom of the methylene group. The structure of 6 is proved by 1,5-H migration giving 8 and autoxidation of the latter at -10°C giving tBuOH and 4-tritylbenzophenone (12). The synthesis of several analogous compounds are described.
    Notes: Die chinoide Titelverbindung 6 entsteht im Gleichgewicht zu 〉95% und kann isoliert werden, wenn die beiden Titelradikale 1 und 3 in Lösung erzeugt werden. Ursache hierfür ist die räumlich günstigere Unterbringung der sperrigen tBu-Gruppe am sp2-C-Atom der Methylengruppe. Die Struktur von 6 wird durch 1,5-H-Verschiebung zu 8 sowie dessen Autoxidation bei -10°C zu tBuOH und 4-Tritylbenzophenon (12) bewiesen. Synthesen analoger Verbindungen werden beschrieben.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19861190621
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  • 2
    Electronic Resource
    Electronic Resource
    Über sterisch gehinderte freie Radikale, XVI. Zur Existenz von Tetraphenylbernsteinsäure und ihrer Ester sowie über die Struktur der Dimeren der Diarylmethyl-Radikale Ar2C⋅ — X, X=CO2R, CN, COR (1986)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 119 (1986), S. 3422-3431 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Sterically Hindered Free Radicals, XVI. The Existence of Tetraphenylsuccinic Acid and Its Esters, and the Structure of the Dimers of the Diarylmethyl Radicals Ar2C⋅—X, X=CO2R, CN, CORAll syntheses of tetraphenylsuccinic acid (esters) described in the literature in fact yield the quinonoids 5 or, after a 1,5-H shift, the benzoids 6.5 dissociates reversibly giving the radicals Ph2C⋅—CO2R 4. A real succinic acid derivative, 9, arises, however, by blocking of the para-positions in 4 by tBu groups (8). The radicals Ph2C⋅—CO—R 14, R=H, Me, Ph, dimerize surprisingly giving neither ethanes nor quinonoids, but via their enoxyls the unstrained novel enol ethers 17. ESR and ΔHdiss values are given and discussed.
    Notes: Alle in der Literatur bekannten Darstellungen von Tetraphenylbernsteinsäure(-estern) führen tatsächlich zu chinoiden Isomeren 5 oder, nach 1,5-H-Verschiebung, zu benzoiden Derivaten 6. 5 dissoziiert reversibel zu Radikalen Ph2C⋅—CO2R 4. Ein echtes Bernsteinsäure-Derivat 9 wurde jedoch erhalten, wenn in 4 die para-Positionen durch tBu-Gruppen blokkiert wurden (8). Radikale Ph2C⋅—CO—R 14, R=H, Me, Ph, dimerisieren überraschend weder zu ethanartigen noch zu chinoiden, sondern über ihre Enoxyle zu ungespannten, neuartigen Enolethern 17. ESR- und ΔHDiss-Werte werden angegeben und diskutiert.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19861191119
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  • 3
    Electronic Resource
    Electronic Resource
    Über sterisch gehinderte freie Radikale, XVII. Über die Addition von Diphenylmethyl-Radikalen an radikophile Olefine und zur Diastereomerenumwandlung von 2,3-Diaryl-2,3-bis(trimethylsilyloxy)bernsteinsäuredinitrilen (1986)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 119 (1986), S. 3432-3441 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Sterically Hindered Free Radicals, XVII. The Addition of Diphenylmethyl Radicals to Radicophilic Olefins, and the Diastereomer Transformation of 2,3-Diaryl-2,3-bis(trimethylsilyloxy)succinonitrilesThe radicals Ph2C⋅—MMe3 2, M=C, Si, Ge, Sn, give with 2-tBuS-acrylonitrile (1) via a 1,4-C,N-addition not known until now exclusively the ketenimine 5, which dissociates reversibly even at 25°C. The less hindered 2-Me3SiO-acrylonitrile (6), on the other hand, undergoes nothing else than the reversible 1,2-addition with 2, M=Si, yielding 7.6 behaves similarly towards the ketyl Ph2C⋅—OSiMe3 (8), whose 1,2-adduct 9, like 7, is useful for further syntheses, e.g. of the ketone 10. The ESR data of the new radicals are given and discussed.  -  The meso/DL diastereomer transformation of the title succinonitriles 13 is evaluated kinetically by means of pure stereoisomers.
    Notes: Die Radikale Ph2C⋅—MMe3 2, M=C, Si, Ge, Sn, reagieren mit 2-tBuS-acrylnitril (1) ausschließlich in einer bisher nicht bekannten 1,4-C,N-Addition zum Ketenimin 5, das bereits bei 25°C reversibel dissoziiert. Das weniger gehinderte 2-Me3SiO-acrylnitril (6) ergibt dagegen mit 2, M=Si, ausschließlich reversible 1,2-Addition zu 7. Ähnlich verhält sich 6 gegenüber dem Ketyl Ph2C⋅—OSiMe3 (8). Dessen 1,2-Addukt 9 kann, wie auch 7, für weitere Synthesen dienen, z. B. zum Keton 10. Die ESR-Daten der neuen Radikale werden angegeben und diskutiert.  -  Die meso/DL-Diastereomeren-Umwandlung der im Titel genannten Bernsteinsäurenitrile 13 konnte anhand von Reinsubstanzen kinetisch verfolgt werden.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19861191120
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  • 4
    Electronic Resource
    Electronic Resource
    Sterically Hindered Free Radicals, 21. 1,2- and 1,4-Additions of Diphenylmethyl Radicals to Substituted Acrylonitriles (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 1179-1185 
    Details
    ISSN: 0009-2940
    Keywords: Radical additions ; Acrylonitriles ; Diphenylmethyl radicals ; Steric effects ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Additions of the substituted diphenylmethyl radicals Ar11-Ar2CR 2 (R=CMe3, SiMe3, GeMe3, SnMe3, OSiMe3, CF3, CO2Me, CN) to various acrylonitriles CH2=C(X)CN 3 (X=SMe, SiPr, StBu, OAc, OSiMe3, OSiEt3, OMe, OEt) lead to 1,2-5 or 1,4-adducts 6 (ketenimines), depending mainly on the steric hindrance by the substituents R and X. Bulky substituents like tBu in 2 and tBuS in the acrylonitrile favour the formation of the extended and nearly strainless ketenimine system 6 (1,4-adduct); smaller substituents like OSiMe3 (radical 2) and SMe, OAc, OSiMe3, OSiEt3, OMe, OEt (acrylonitrile) allow isolation of the sterically crowded 1,2-adducts. Substituents of intermediate bulkiness like CF3 (radical 2) and SiPr (acrylonitrile) give a mixture of 1,2-adducts (6cb, hb) and dimers 7 of the adduct radicals 4 (7cb, hb). The voluminous tBu group directly bound to the olefin (3j,k) prevents addition. The latter is generally reversible, and the various adducts 5, 6, or 7 dissociate to the adduct radicals 4 and/or fragment to the initial radicals 2 at temperatures which reflect the steric strains of the corresponding substituents R, X. The complete inertness, even toward the electron-rich olefin 3i, of the electrophilic α1-carbonyl-substituted radicals 2q - s (R=CHO, COMe, COPh) in the above additions is discussed. Additions of the radicals 2a - c, f, i, n, o to the conjugated olefin 3n are described and are in accordance with the conclusion that steric effects predominate in adduct formation, whereas electronic effects are of distinct but minor importance.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260518
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