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  • 1
    Electronic Resource
    Electronic Resource
    Stereochemistry of tetrahedral nickel complexes. Configurational rigidity and stereochemical analyses (1977)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 99 (1977), S. 650-651 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00444a076
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  • 2
    Electronic Resource
    Electronic Resource
    1H-Kernresonanzverschiebungen in der Gerüstebene anisotroper CO-, CN- und CC-Doppelbindungen (1979)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 112 (1979), S. 3490-3514 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: 1H NMR Shifts in the Molecular Planes of Anisotropic CO, CN, and CC Double BondsSynthetic procedures are given for fluorenes with 2,7- and 1,8-dimethyl as well as 2-fluoro and 2,7-difluoro substituents. Analysis and comparison of the NMR spectra provides evidence of downfield shifts for protons situated in the planes of doubly bonded moieties with reference to compounds devoid of such double bonds. Tetralin and indan derivatives lead to corresponding conclusions. The importance of conjugation and of electric field effects is assessed by protonation studies.
    Notes: Die Synthese von Fluorenderivaten mit 2,7- und 1,8-Dimethyl- sowie 2-Fluor- und 2,7-Difluor-Substituenten wird beschrieben. Durch Analyse und Vergleich ihrer NMR-Spektren zeigt sich, daß 1H-Atomkerne in Doppelbindungsebenen bei geringeren Magnetfeldstärken absorbieren als in Vergleichsverbindungen ohne entsprechende Doppelbindung. Modellverbindungen mit Tetralin- und Indan-Struktur führen zum gleichen Schluß. Die Bedeutung konjugativer Substituenteneinflüsse und elektrischer Feldeffekte wird anhand von Verschiebungsänderungen bei der Protonierung beurteilt.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19791121017
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  • 3
    Electronic Resource
    Electronic Resource
    Azomethine, 1-Azaallyl-Anionen und metastabile sek. Enamine (1980)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 113 (1980), S. 2462-2489 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Azomethines, 1-Azaallyl Anions, and Metastable Secondary EnaminesE/Z equilibrium constants of the ketone anils 6a-s do not depend significantly on the inductive substituent effect. 1H NMR chemical shifts used for configurational classification are also effective for assignments in comparable, isomerically almost pure azomethines 6aa-pp and may be explained by the anisotropic shift model. The 1-azaallyl anions 7 prepared by deprotonation are characterized by 1H NMR spectroscopy. Kinetic and thermodynamic control of this metallation reaction result in different preferential configurations of such anions, the methanolysis of which yields metastable sec. enamines 8 by regio- and stereospecific N-protonation. It is possible to estimate further substituent parameters λd from E/Z equilibria.
    Notes: Die E/Z-Gleichgewichtskonstanten der Keton-anile 6a-s hängen nicht wesentlich vom induktiven Substituenteneffekt ab. Die für eine Zuordnung geeigneten 1H-NMR-Verschiebungen gelten auch für vergleichbare, meist isomerenfreie Azomethine 6aa-pp und gehorchen dem Anisotropiemodell. Durch Metallierung entstehen die 1-Azaallyl-Anionen 7; diese werden 1H-NMR-spektroskopisch charakterisiert. Kinetische und thermodynamische Reaktionslenkung führen zu unterschiedlichen Vorzugskonfigurationen dieser Anionen; die Methanolyse liefert metastabile sek. Enamine 8 unter regio- und stereospezifischer N-Protonierung. Aus den E/Z-Gleichgewichtslagen lassen sich weitere Substituentenparameter λd abschätzen.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19801130714
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  • 4
    Electronic Resource
    Electronic Resource
    Der konformative ortho-Effekt bei o-Tolylstilbenen und deren Vinyllithiumderivaten1,2) (1981)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 114 (1981), S. 1581-1591 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The Conformational ortho-Effect ino-Tolylstilbenes and their vinyllithium Derivatives1,2)Geometrical isomers of stilbene derivatives with an additional, o-substituted phenyl moiety at the CC double bond (5, 6, 13) are prepared and structurally assigned. The isomer with the two phenyl groups in trans-position is favoured in equilibrium (conformational ortho-effect). For the vinyllithium derivative (19/20), a strong solvent dependency of 1H NMR shifts and of the rate of equilibration if found.
    Notes: Geometrische Isomere von Stilbenderivaten mit o-substituiertem Phenyl als zusätzlichem Substituenten an der CC-Doppelbindung (5, 6, 13) werden hergestellt und strukturell zugeordnet. Das Isomere mit trans-ständigen Phenylgruppen ist im Gleichgewicht begünstigt (konformativer ortho-Effekt). Beim Vinyllithiumderivat (19/20) hängen die 1H-NMR-Verschiebungen und die Geschwindigkeit der Gleichgewichtseinstellung stark vom Lösungsmittel ab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19811140502
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  • 5
    Electronic Resource
    Electronic Resource
    Zur Bildung und Reaktivität di-tert-alkylsubstituierter Phenylalkene (1980)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1980 (1980), S. 1207-1215 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: On the Formation and Reactivity of Di-tert-alkyl Substituted PhenylalkenesMolecular rearrangements occur during the attempted syntheses of α-bromo-β,β-di-tert-alkylstyrenes; the resulting structures are elucidated. A hydrocarbon dimer with allenic structure accompanies the formation of the Grignard reagent from an α-bromostyrene with bulky substituents.
    Notes: Bei Versuchen zur Synthese von α-Brom-β,β-di-tert-alkylstyrolen laufen molekulare Umlagerungen ab; die Strukturen der Reaktionsprodukte wurden aufgeklärt. Bei einem sperrig substituierten α-Bromstyrol ist die Bildung der Grignardverbindung von der eines dimeren Kohlenwasserstoffs mit Allenstruktur begleitet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198019800805
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  • 6
    Electronic Resource
    Electronic Resource
    (EIZ)-Equilibria, 19 Part 18: Ref.[19].  -  [*I X-ray structural analyses. Dimeric α-Lithio-2,6-dimethylstyreneDedicated to Prof. Joseph Klein on the occasion of his 80th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 585-592 
    Details
    ISSN: 0009-2940
    Keywords: Aggregations ; Complex, tert-butyl methyl ether ; diastereotopomerization, (EIZ) ; NMR, coupling, constants, HH, CH, CLi ; NMR, Lithiation shifts ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Improved preparations of 2,6-dimethylstyrene (5) and its α-bromo derivative (10) are described. The Br/Li exchange reaction of 10 provides single crystals of the title compounds 11 or 12, which were characterized as disolvated dimers by X-ray analyses. A similar dimer persists in diethyl ether, tert-butyl methyl ether, and toluene at all accessible temperatures, with significant lithiation NMR shifts (relative to 5) partially due to charge delocalization from the sp2-carbanionic center. Some NMR coupling constants are typical of the dimeric aggregate. The configurational (E,Z) lability is quantified in toluene solution.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300509
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  • 7
    Electronic Resource
    Electronic Resource
    Sterically Congested Molecules, 11. The 2,6-Diisopropylphenyl Substituent at C=C and C=N Groups (1994)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1994 (1994), S. 433-438 
    Details
    ISSN: 0170-2041
    Keywords: Aryl group, rotation ; Cuprates ; Diastereotopomerization ; Hydrazones ; Styrene derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two series of new compounds with sterically shielded, sp2-hybridized C-α atoms are prepared from bromo(chloro)-2,6-diisopropylbenzene. The α-(2,6-diisopropylphenyl) substituent common to all of them is used as an NMR-spectroscopic indicator for the ease of aryl-α single-bond rotation. The corresponding ΔG≠ values are 〉23.8 kcal/mol with methyl or bromine as additional α substituents at a C=C bond, but 〈8.5 kcal/mol with α-H. The analogous 2,6-diisopropylacetophenone imine has ΔG* = 18.0 kcal/mol while the N-substituted imines prefer the (Z) conformations with ΔG≠ 〉 23.3 kcal/mol, and ΔG≠ ≈ 31.5 kcal/mol for the (Z)-hydrazone. Comparisons of these data with reaction conditions show that chemical transformations are not seriously impeded unless they depend on reagent attack at a π face of the C-α atom in a C=C or C=N group which rotates slowly about the bond to 2,6-diisopropylphenyl.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199419940417
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