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  • 1
    Electronic Resource
    Electronic Resource
    (E,Z) Equilibria, 12. Differential NMR Shielding by Phenyl, Assigned from Chemical Labelling and (Z,E) Equilibration (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1137-1141 
    Details
    ISSN: 0009-2940
    Keywords: Allyl anion ; Differential NMR-shielding ; Schiff's bases ; Stereoselective substitution ; Isomerization, (Z,E) ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unequivocal NMR assignments of the (E,Z) isomeric pairs 3 and 8 are possible by (Z,E) equilibration. Deprotonation of 2-methyl-1-phenylpropene (1) with n-BuLi under any conditions gives only a single allyl-metal derivative 2. Methylation of the latter gives the isomer (Z)-3, while deuteriolysis leads to the isotopically labelled derivative 6 of the olefin 1; this Proves the NMR assignments for 1 as well as the endo configuration of 2. The phenyl group gives rise to a differential shielding effect on the γ-carbon nuclei in methyl and methylene gropus along a CC double bond (ca, 7 ppm), and this effect is comparable to that along a CN double bond as in 8. The nitrile function in 5c is much less effective.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230529
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  • 2
    Electronic Resource
    Electronic Resource
    Cyclopropan-Derivate, 2. Selbst-Acylierung der α-Alkyl-γ-lactone zu Herstellung von Bis(1-alkylcyclopropyl)ketonen über Spiro[4.4]acetale (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2161-2166 
    Details
    ISSN: 0009-2940
    Keywords: Acetals ; Ketones ; γ-Lactones ; Butanolides ; Spiro compounds ; Cyclopropyl compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclopropane Derivatives, 2.  -  Self-Acylation of α-Alkyl-γ-lactones To Give Bis(1-alkylcyclopropyl)ketones via Spiro[4.4]acetalsHigh-yield synthetic ways are recommended for the title lactones 1.The coupling of two 2-alkyl-4-butanolides is possible in an inter-(1b, c) or intramolecular fashion (4c) to give spiro[4.4] acetals 8 or 9 respectively, in the absence of hindering substituents. Symmetrically substituted bis(1-alkylcyclopropyl)ketones 12 and 13 may be prepared by acidic cleavage of those spiro[4.4] acetals lacking 2,7-substituent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901231112
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  • 3
    Electronic Resource
    Electronic Resource
    (E,Z)-Gleichgewichte, 15. Synthesen und erhöhte Konfigurationslabilität von 2-Iminoindan-Derivaten mit Vorderseitenspannung (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 2041-2049 
    Details
    ISSN: 0009-2940
    Keywords: Basicity ; Diastereotopomerization, (E/Z) ; Imines ; Steric shielding ; Steric strain ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (E,Z) Equilibria, 15[1]. - Syntheses and Lability of the Configuration of 2-Iminoindan Derivatives with Front StrainSyntheses and properties are described for sterically shielded imines R2C = NR (3c, e, g-k), which are rather inert toward nucleophiles. Nucleophilic attack at the nitrogen atom of 3k is indicated by the formation of the azine 4. (E,Z) Configurational diastereotopomerization (anti/syn) is strongly dependent on N substituents [CH3, phenyl, 1-naphthyl, acetyl, Si(CH3)3, cyano, SC6H5, SOC6H5, SO2C6H5, and nitro]. It is accelerated by front strain along the C—N bond in 3a-c, e, g, h, j, and k and provides an energetic basis (by ΔG≠ and ΔΔG≠ values) for the gauging of force-field parameters. This (E,Z) stereo-mutation is characterized by a vanishing solvent dependence and a positive volume of activation (+10.2 cm3 mol-1 for 3a). In contrast to other π acceptor substituents, the N-nitro group in 31 retards (E,Z) interconversion.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250912
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  • 4
    Electronic Resource
    Electronic Resource
    (E,Z) Equilibria, 14. Substituent-Induced Chemical Shifts along the C = N Bond of Schiff Bases (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 2033-2040 
    Details
    ISSN: 0009-2940
    Keywords: 13C NMR, SCS ; Substituent effects ; Imines ; Isomerization, (E,Z) Schiff bases ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sterically congested N-(1,1,3,3-tetraalkyl-2-indanylidene)-amines 8-11, N-(cyclopentylidene)anilines 13-17, and two of their salts are described, together with a short synthesis of 2-imino-1,1,3,3-tetramethylindan (5). Some of these imines show rapid (E,Z) equilibration. Positively and negatively charged nitrogen functions (in 6 and 7) cause opposite 1H- and 13C-NMR chemical shift effects along the C = N bond. Chemical shifts are almost equally affected by the lone electron pair and by the imino N-H bond. Substituent-induced chemical shifts (SCS) have been assigned for all syn and anti positions with respect to methyl, phenyl, and 2,6-dimethylphenyl groups at the imino nitrogen atom. The structurally well-defined, rigid imines recommend themselves as new models for the calibration of theoretical approaches to syn/anti-differentiating SCS.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250911
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  • 5
    Electronic Resource
    Electronic Resource
    (E, Z)1-Equilibria, 17 Demonstration of the Nitrogen Inversion Mechanism of Imines in a Schiff Base ModelDedicated to Professor Heinrich Nöth on the occasion of his 65th birthday. (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 747-754 
    Details
    ISSN: 0009-2940
    Keywords: Diastereotopomerization, (E, Z) ; Imines ; Inversion, nitrogen ; Permethylation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experimental differentiation between pure C=N double bond rotation and nitrogen inversion in N1-arylimines is possible with a single compound (13b) under the proviso of slow rotation about the N-aryl single bond. Labelling by 1H and 13C nuclei at the diastereotopic faces of the C=N moiety as well as of the N-aryl group is the clue to a successful stereodynamic analysis, as performed by variable-temperature NMR spectroscopy of 13b, a sterically congested and chiral model compound. Interpretation of similar measurements on a second model (13d) is less straightforward. The experimental observation of time-averaged Cs symmetry by NMR coalescences is only compatible with a mechanism of (E/Z) stereomutation either by pure inversion at sp2 nitrogen or by a contribution from C=N rotation together with a synchronized (geared) controtation about the N-aryl single bond. However, the latter combination is concluded to be predominantly inversion-like by comparisons with related imines.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260327
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  • 6
    Electronic Resource
    Electronic Resource
    Erschöpfende α-Alkylierung von Fünfring-Ketonen mit Natriumhydrid und Dimethylsulfat oder Ethyliodid (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 1791-1793 
    Details
    ISSN: 0009-2940
    Keywords: Cycloalkanones ; Dimethyl sulfate ; Peralkylation ; Sodium hydride ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Exhaustive α-Alkylation of Five-Membered Ring Ketones by Sodium Hydride and Dimethyl Sulfate or Ehtyl IodideCα-Permethylation may be carried out by addition of a basesensitive ketone like cyclopentanone to the inexpensive and stable mixture of sodium hydride and dimethyl sulfate. Exhaustive Cα-ethylation is exemplified with sodium hydride by simultaneous introduction of ketone 4 and ethyl iodide. The 13C-NMR absorptions of 1,3-alkylated 2-indanones 3-5 are assigned and some of the CH coupling constants reported.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891220927
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  • 7
    Electronic Resource
    Electronic Resource
    Cyclopropan-Derivate, 3. (1-Alkylcyclopropyl)ketone durch Acylierung von α-substituierten γ-Lactonen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2167-2172 
    Details
    ISSN: 0009-2940
    Keywords: Acylation ; Ketones ; γ-Lactones ; Butanolides ; Cyclopropyl compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclopropane Derivatives, 3.  -  (1-Alkylcyclopropyl)ketones by Acylation of α-Substituted γ-LactonesThe 2-acylation of 2-substituted 4-butanolides 2 is moderately sensitive to steric crowding, whereas the subsequent ring- opening of 2-acyl-2-alkyl-4-butanolides 4, 11 to give-chloro ketones 6, 12 by chloride-transferring acid derivatives be-comes difficult with bigger lactone substituents. Similar observations pertain to the preparation of y-chlorobutanoyl chlorides 10 from 2-alkyl-4-butanolides 2. The proper choice of the starting 4-butanolides (2a, b or 14 but not 2c) provides for an indirect coupling of two different lactones to y,y-dichloro ke-tones 12. Dicyclopropyl ketones 13 with variable patterns of substitution may thus be prepared from 4-butanolides in a direct manner with global yields exceeding 50% and without purification of intermediate products (except for acid chlorides like 10).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901231113
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