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  • 1
    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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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    1H NMR lanthanide-induced shift (LIS) investigations of highly flexible molecules - a new approach. Part IIFor Part I, see Ref. 1. (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 367-370 
    Details
    ISSN: 0749-1581
    Keywords: 1H NMR ; Lanthanide-induced shift (LIS) ; Conformational analysis of highly flexible molecules ; Steepest descent (STEED) LIS calculation algorithm ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method and computer program for LIS calculations of highly flexible molecules was developed using molecular geometries obtained by randomly varied dihedral angles (up to ten angles rotating freely and independently from each other are possible) as start conformations for a STEEpest Descent (STEED) search algorithm to find minima characterized by the R factor at the ‘LIS R factor hyper surface.’ This STEED-LIS method allows easy, accurate and rapid access to the probable global minimum of the R factor depending on up to ten variable dihedral angles. This means that LIS investigations of highly flexible molecules with more than one freely rotating dihedral angle are no longer complicated and time consuming, but can be carried out automatically using the developed programs [JLLISSD (with interactive parameter dialogue) and LISSDEMU (using parameter input files prepared by LISSDINP)]. The results obtained are in very good agreement with known or reported preferred conformations of the investigated test compounds, propan-1-ol, butan-1-ol and ethyl p-methoxycinnamate.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260310411
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