Abstract
High-resolution ESR spectra of the ground-state negative ions of hexafluoro cyclopropane (c-C3F6.-), octafluorocyclobutane (c-C4F8.-), and decafluorocyclopentane (c-C5F10.-) are reported and their isotropic 19F hyperfine coupling constants (hfcc) of 198.6 ± 0.4 G, 147.6 ± 0.4 G, and 117.9 ± 0.4 G, respectively, are in inverse ratio to the total number of fluorine atoms per anion. Together with the small value of 5.2 ± 0.4 G determined for the isotropic 13C hfcc of c-C4F8.-, these results indicate that in each case the singly occupied molecular orbital (SOMO) is delocalized over the equivalent fluorine's and possesses a nodal plane through the carbon atoms of a time-averaged Dnh, structure. A series of quantum chemical computations were carried out to further characterize these anions and their neutral counterparts. Both the B3LYP density functional and second-order Møller-Plesset perturbation theory (MP2) indicate that c-C3F6.- adopts a D3h, geometry and a 2A2″ ground electronic state, that c-C 4F8.- adopts a D4h, geometry and a 2A2u ground electronic state, and that c-C 5F10.- adopts a Cs structure and a 2A′ electronic state. Moreover, the 19F hyperfine coupling constants computed with the MP2 method and a high-quality triple-ζ basis set are within 1% of the experimental values. Also, the values computed for the 13C hfcc of c-C4F8.- are consistent with the experimental value of 5.2 G. Therefore, in keeping with the ESR results, these negative ions derived from first-row elements can be characterized as π* species. In addition, the hyper valency of these perfluoro cycloalkane radical anions has been clarified. © 2005 American Chemical Society.
Recommended Citation
A. M. Elsohly et al., "Computational and Esr Studies of Electron Attachment to Decafluorocyclopentane, Octafluorocyclobutane, and Hexafluorocyclopropane: Electron Affinities of the Molecules and the Structures of their Stable Negative Ions as Determined from ¹³c and 19f Hyperfine Coupling Constants," Journal of the American Chemical Society, vol. 127, no. 30, pp. 10573 - 10583, American Chemical Society, Aug 2005.
The definitive version is available at https://doi.org/10.1021/ja0505898
Department(s)
Chemistry
International Standard Serial Number (ISSN)
0002-7863
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2024 American Chemical Society, All rights reserved.
Publication Date
03 Aug 2005
