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

Abstract

High-resolution ESR spectra of the ground-state negative ions of hexafluorocyclopropane (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 fluorines and possesses a nodal plane through the carbon atoms of a time-averaged D(nh) 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 D(3h) geometry and a (2)A2'' ground electronic state, that c-C4F8*- adopts a D(4h) geometry and a (2)A2u ground electronic state, and that c-C5F10*- adopts a C(s) structure and a (2)A' electronic state. Moreover, the 19F hyperfine coupling constants computed with the MP2 method and a high quality triple-zeta 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 pi* species. In addition, the hypervalency of these perfluorocycloalkane radical anions has been clarified.

Applications of EPR and ENDOR Spectrum Simulations in Radiation Research

“…The experimental spectra of the C 4 F 8 − radical anion at increased temperature were in fact similar to the simulated one in Fig. 19.4 [34,35]. [34,35] for comparison with the experimental spectra in the γ-irradiated HME and TMS matrices…”

“…19.4 [34,35]. [34,35] for comparison with the experimental spectra in the γ-irradiated HME and TMS matrices…”

“…Radical anions formed by radiation induced electron attachment to perfluorocycloalkanes in frozen matrices have been investigated experimentally and theoretically [34,35]. Nearly isotropic EPR spectra were observed in hexamethylethane (HME) and tetramethylsilane (TMS) matrices.…”

5-Fluorolysine as alternative substrate of lysine 5,6-aminomutase: A computational study

“…Accurate theoretical prediction for the 19 F HFCCs values seems difficult. Authors have employed several combinations of methods and basis sets to calculate 19 F HFCCs [56][57][58]. Nevertheless, it is yet not well established which method and basis sets predict accurate 19 F HFCCs.…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 17, 2006) and the discipline

“…The results of Rademacher's study confirmed the general applicability of the two-orbitals model for the relationship between geometrical and electronic structures for substituted cyclopropanes, yet experimental verification of the totality of these findings by photoelectron spectroscopy is highly desirable. Much as the ionization energies of these fluorocyclopropanes are thus of interest, so have the related electron affinities [21][22][23]. Enthalpies of formation from the experimental literature of neutral fluorinated cyclopropanes are seemingly limited to those of the hexafluoro and 1,1,2,2-tetrafluorinated species, and even here there are complications in interpretation and analysis [24].…”