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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 821-826 
    ISSN: 0009-2940
    Keywords: α-Diketones, unsaturated ; Conformers, stable ; UV-Vis transition energies ; PE Spectroscopy ; 13C-NMR chemical shifts, correlation with dihedral angles CO/CO ; Calculations, STO-3G, MMP1 ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromophoric Systems, 1.  -  Conformation and Absorption of Light in Hexa-1,5-diene-3,4-dione (Divinylglyoxal)Divinylglyoxal (1) is investigated by several spectroscopic and theoretical methods in order to set up a correlation between the CO/CO dihedral angle and the transition energies in unsaturated α-diketones. According to the experimental (UV, IR, 13C-NMR, PE spectroscopy and dipole moment) and theoretical (ab initio and molecular mechanics) results, 1 exists predominantly as a C2h conformer (Θco/co=180°, ΘVinyl/co=0°). The dependence of transition energies on CO/CO dihedral angles is similar in shape to that for saturated α-diketones, but is significantly shifted to lower transition energies. 13C chemical shifts respond sensitively to CO/CO dihedral angles, and the ab initio calculated curve is supported by a few experimental results.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0009-2940
    Keywords: Lone-pair orientation ; Lone pair interaction ; Precanonical orbitals ; Orbitals, localized ; Calculations, ab initio STO-3G, MNDO, MM2 force field ; PE Spectroscopy ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The He(I) photoelectron spectra (PE) of 7-azanorbornane (5), 7-azanorbornene (6), and 7-azanorbornadiene (7) as well as of related urethanes have been recorded. The syntheses of these bicyclic compounds are described in detail. A most convenient analysis of the PE spectroscopic results is based on the procedure of Heilbronner-Schmelzer on an ab initio STO-3G level. This method allows to construct fragment orbitals elucidating the orientation of the nitrogen lone pair, the through-space interaction with π bonds, and the participation of σ bond orbitals. The result is remarkable: whereas the direct interaction of localized lone-pair and π orbitals is significant in both syn;- and anti-orientation, the interaction of a localized lone pair with a precanonical fragment π orbital is completely different in the two geometries. In 6;-syn a considerable interaction matrix element FantiΨnπ=-0.71 eV comes to the fore, whereas the corresponding parameter in 6;-anti turns out to be almost zero, FantiΨnπ=+ 0.09 eV. Since 6;-syn is calculated to be more stable than 6;-anti, it is this invertomer, 6;-syn, which is likely to be responsible for the main bands in the PE spectrum of 6. The comparatively large experimental split between the first two PE bands of 6 (0.98 eV) is in accord with the 6;-syn geometry and compares well with the calculated band separation of 1.26 eV for 6;-syn.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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