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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 409-417 
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We have developed a molecular modeling procedure to determine the relative configuration of a chiral molecule from nuclear magnetic resonance (NMR) data. Our procedure uses constrained molecular mechanics, and the constraints are interproton distances derived from the experimental nuclear Overhauser enhancement (NOE) data. The main feature is a period of high-temperature dynamics in which frequent inversions occur at most chiral sites. This allows the distance constraints to guide the molecule into configurations consistent with the NOE data. For molecules with complex ring systems, high-temperature dynamics alone may fail to invert certain chiral centers with sufficient frequency. We have countered this by allowing as an option additional inversions of selected chiral centers. The procedure tested successfully on organic molecules of known stereochemistry, with 5 to 17 chiral centers, provided that the number of available constraints was at least twice the number of chiral centers. The procedure is tolerant of large errors in the estimated interproton distances and is reasonably rapid. For a series of sugars, the time required increases less than quadratically with the number of atoms. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 21 (1990), S. 563-567 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The bending fundamentals ν2 of the three isotopic species of water, H2O, D2O and HDO, were examined in the infrared spectra of liquid water at 0-99.9% D. The peak positions of the three bands vary linearly with the molar fractions of the three isotopic species. The half-widths of ν2 of H2O surrounded by D2O and of D2O surrounded by H2O, which are largely free from vibrational coupling, have been whown to reflect the distrbution of instantaneous hydrogen-bond strengths in liquid water. The contribution to the ν2 band width from dynamic processes is relatively small. Vibrational coupling, in the spectra of isotopically pure H2O or D2O, leads to additional broadening and to a sizable shift of the band center to lower frequencies. Small band shifts confirm that weak vibrational coupling also occurs between HDO and H2O and H2O and between HDO and D2O.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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