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  • 1
    Electronic Resource
    Electronic Resource
    1H NMR lanthanide-induced shift investigation of highly flexible molecules - a new approach (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 68-70 
    Details
    ISSN: 0749-1581
    Keywords: 1H NMR ; Lanthanide-induced shift (LIS) method ; Conformational analysis of highly flexible molecules ; Calculation algorithm ; Molecular mechanics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method for lanthanide-induced shift (LIS) calculations of highly flexible structures was developed using molecular geometries obtained from the random variation of dihedral angles (up to ten) which are rotating freely and independently of each other. The result of the new method (program JLLISMUL) is a data set containing the specified random dihedral angles and the corresponding agreement factor R (as a criterion for the fitting of the calculated and experimental LIS values). For comparison, the same random procedure was also used for parallel force field calculations using the molecular mechanics program PIMM. The results obtained by the new method are in very good agreement with known or reported preferred conformations of five highly flexible molecules which were used as examples for examining the new strategies of obtaining the preferred conformers. The minima of both the ‘LIS R factor hyper surface’ and the ‘energy hyper surface’ are rapidly accessible.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260310114
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  • 2
    Electronic Resource
    Electronic Resource
    Stereochemistry of crown ethers. V.For Part 4, see S. Stoss, E. Kleinpeter and H.-J. Holdt, Magn. Reson. Chem. 29, 999 (1991). - solution structure and complexational behaviour of dibenzo crown ethers (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 425-433 
    Details
    ISSN: 0749-1581
    Keywords: Dibenzo crown ethers ; Conformations ; NMR ; Molecular mechanics ; Alkali complexes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preferred conformations and the complexing behaviour of 16- and 17-membered dibenzo crown ethers were studied by means of both NMR spectroscopy and molecular mechanical calculations. Conclusions could be drawn about the stoichiometry and stability of the alkali metal ion corand complexes. The spin-lattice relaxation times of the crown ether carbon atoms and the relevant complexes are discussed with respect to the intramolecular flexibility of these species. The intramolecular reorientations detected are reduced considerably in the alkali metal ion complexes. In the preferred conformers of corands 2, 3 and 6, the molecular mechanical calculations prove that the phenyl rings are positioned in a chair conformation at a twist to each other. The same phenyl rings in the crown ethers 1, 4 and 5 are in a boat conformation. These conformations seem to be important for the optimum complexation of the alkali cations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300514
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  • 3
    Electronic Resource
    Electronic Resource
    Conformational study of the 4,9-dihetero-(Z,Z)-cyclodeca-1,6-diene ring system; the mono- and di-benzo analogues (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 628-634 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR ; 1H NMR ; 4,9-Dihetero-(Z,Z)-cyclodeca-1,6-dienes ; Ring inversion barriers ; Restricted rotation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dynamic 1H and 13C NMR spectra of a series of mono- and bis-annelated 4,9-dihetero-(Z,Z)-cyclodeca-1,6-dienes were obtained and are discussed with respect to ground-state conformers and the barriers to ring inversion, and to the restricted rotation about exocyclic partial C,N double bonds. The ten-membered rings are, with one exception, anancomeric chair conformers and interconvert via a combination of single bond rotations and bond angle bendings. Depending on the heteroatoms present, the series of decreasing barriers to ring inversion S 〉 NH 〉 O was obtained. Benzannelation decreases the free energy of activation of the same dynamic process owing to greater intramolecular transannular H,H interactions.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260280713
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  • 4
    Electronic Resource
    Electronic Resource
    Study of the distribution of the π-electrons in push-pull alkenes by 1H and 13C NMR spectroscopy (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 212-222 
    Details
    ISSN: 0749-1581
    Keywords: Dynamic NMR ; 13C NMR ; Push-pull alkenes ; Restricted C,C and C,N rotation ; π-Electron density distribution ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Push-pull alkenes with variable structure were investigated with respect to the influence of the different substituents at the central C,C double bond on the dynamic behaviour of this type of compound. 1H and 13C NMR spectroscopic investigations were carried out for ketene-S,S-, -S,N- and -N,N-acetals. HMO calculations were employed to discuss the related π-electron density distributions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290305
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