Intramolecular screening effects on nuclear magnetic resonance chemical shifts. Part IV. The fluorine-19 resonance spectra of some bridgehead-substituted fluorobicyclo[2,2,1]heptanes

Abstract

The ¹⁹F resonance spectra of some bridgehead-substituted fluorobicyclo[2,2,1]heptanes are reported and analysed to give approximate values for chemical shifts and geminal fluorine coupling constants. The ¹⁹F shifts for 1H-undecafluoro- and 1H, 4H-decafluorobicyclo[2,2,1]heptane are calculated by use of an intramolecular electric field approach and found to be consistent with those observed. The apparently anomalous trends in observed shifts with the electronegativity of the substituents in a series of fluorobicyclo[2,2,1]heptanes are also discussed in terms of electric fields.