Proton Magnetic Resonance Spectrum of Parafluorotoluene. Sigma and Pi Electron Contributions to JpH,F

The p.m.r. spectrum of a 15 mole % solution of p-fluorotoluene in acetone-d6 is analyzed at 100 MHz using LAOCN3 and LAME computer programs. The resulting spectral parameters satisfactorily reproduce the methyl proton resonance at 60 MHz. The coupling over six bonds between the fluorine nucleus and the methyl protons is 1.15 ± 0.02 Hz and is taken as a measure of the π electron contribution to the coupling over five bonds between the fluorine nucleus and the proton in p-fluorobenzene. The σ electron contribution to this coupling is discussed for some fluorobenzene derivatives and is shown to depend on the electronegativity of the substituents in a manner completely analogous to proton–proton and other proton–fluorine couplings in benzene and pyridine derivatives.