¹H and ¹³C spectra of fluorine‐containing polycyclic aromatic hydrocarbons. ¹H¹⁹F and ¹³C¹⁹F coupling across bay regions

Abstract

Abstract The 1 H and 13 C NMR spectra of several fluorine‐substituted polycyclic aromatic hydrocarbons in which fluorine projects into a bay region were studied. Both protons and carbons of the sterically opposed CH bond show anomalously large F‐induced shifts and couplings to fluorine. The magnitudes of the couplings (particularly the four‐bond CF couplings which average 26 Hz) indicate a large through‐space contribution due to direct overlap between fluorine and CH bond orbitals, whereas the F‐induced shifts seem more likely to stem from diamagnetic anisotropy rather than F‐induced CH bond polarization.