The spin–spin coupling over six bonds between19F and13C nuclei on the sidechain in thirteen 4-fluorophenyl derivatives appears to be mediated by a σ–π mechanism. Its magnitude depends somewhat on the hybridization state of the carbon atom carrying the coupled nucleus, as well as on the electronegativity of substituents attached to this carbon atom. A consistent behaviour of this coupling is observed if its value is assumed to be proportional to sin2θ, where θ is the angle by which the bond carrying the coupled carbon nucleus twists out of the ring plane. However, in 4-fluorostyreneis a π electron coupling in the planar form, so that its magnitude decreases as the vinyl group twists out of the benzene plane. The σ–π contribution to this coupling is smaller than the π component.is used to assess the conformational preferences of a number of compounds, including 4-fluoro-α-methylstyrene, 4,4′-difluorodiphenylmethane, 1,1-dichloro-2,2-bis(4-fluorophenyl)ethane, and 1-(4-fluorophenyl)-N-methylcyclohexylamine.