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  • Computational Chemistry and Molecular Modeling  (1)
  • stereoelectronic effect  (1)
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  • 1
    ISSN: 0947-6539
    Schlagwort(e): ab initio calculations ; conformation ; microwave spectroscopy ; pyridines ; stereoelectronic effect ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: One single conformer was assigned from the microwave spectrum of 2-(fluoromethyl)pyridine, investigated in the gas phase in the 26.0-39.0 GHz spectral region at about -10°C. Its Cα-F bond was found to be coplanar with the ring and anti to the N-C2 bond (syn to the C2-C3 bond). There was no indication in the microwave spectrum of the presence of other rotameric forms of the molecule.The results of the spectroscopic study were backed up by ab initio calculations at the MP2/6-31 G** (frozen core) level. These calculations predict that the assigned conformer is the only stable form of the molecule. The transition state was calculated to have the CH2F group 180° from the stable anti conformation. The energy of the transition state was computed to be 20.2 kJ mol-1 higher than the energy of the anti rotamer.The results are interpreted in terms of a stereoelectronic effect, and the orbital overlaps responsible for the observed effect are discussed. It is shown that 2-(fluoromethyl)pyridine serves as a good model for 2-(alkoxymethyl)pyridines, previously found to show the same conformational preference.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 0192-8651
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Biochemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Informatik
    Notizen: The conformational preferences of oxymethylpyridines have been investigated by ab initio calculations and compared to similar calculations for oxymethylbenzene. The C—O bond in the pyridine compounds was found to prefer eclipsing with a C—C bond in the ring, in agreement with previous observations but in disaccord with tentative MM2 calculations. The effect was most pronounced in the 2-substituted pyridine. The benzene compound, on the other hand, showed good agreement between the energies from MM2, MM3, and ab initio calculations. The conformational preferences are discussed in terms of stereoelectronic interactions. New MM2 and MM3 parameters were determined from ab initio calculations on nonstationary points on the energy hypersurface. The parameterization method is discussed. © 1995 by John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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