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
URL:
http://dx.doi.org/10.1002/cber.19911240420
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