DFT-GIAO and DFT-NBO studies of the origin of 19F NMR shielding effects in alkyl fluorides

William Adcock, Dieter Lünsmann, Juan E. Peralta, Rubén H. Contreras

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Electron delocalization into the local environment of the fluorine nucleus in the anti (1) and syn (2) epimers of 7-norbornenyl fluoride, 7-fluoronorbornane (3), 7-fluoronobornadiene (4) and the equatorial and axial epimers of cyclohexyl fluoride (5 and 6, respectively) were studied using the natural bond orbital (NBO) approach. The level of theory, B3LYP/6-311G**, was chosen in such a way that the GIAO-calculated 19F magnetic shielding constants in all these compounds were in very good agreement with experimental values. The large 19F deshielding effects known experimentally in 1 and 4 with respect to 2 and 3 are rationalized in terms of differences in such electron delocalizations. The main contribution is that corresponding to the π → (C-F)* interaction, which is only efficient for an anti orientation of the C-F bond and the vinyl moiety. 19F and 13C NMR spectra of 5 and 6 were also measured because some ambiguity was detected in the literature. Despite the large calculated charge donation to the fluorine environment in 6, its 19F resonance appears upfield from that in 5. This trend is rationalized as originating in γ effects of the C-Hax bonds of the kind which have been invoked to explain 17O chemical shift trends in different cyclohexanols and their respective ethers. Electron delocalization effects on 1J(C,F) and 2J(C,F) couplings are also discussed.

Original languageEnglish
Pages (from-to)167-172
Number of pages6
JournalMagnetic Resonance in Chemistry
Issue number3
StatePublished - Mar 1999


  • 7-norbornenyl fluorides
  • Cyclohexyl fluorides
  • F NMR
  • F chemical shifts
  • J(C,F)F and J(C,F) couplings
  • NMR


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