The nuclear magnetic resonance spectra of fluorobenzenes. Part III. o-Difluorobenzene and some 1-substituted 2,3-difluorobenzenes

Abstract

The AA′BB′XX′ spectrum of o-difluorobenzene and the ABCRX spectra of some 1-substituted 2,3-difluorobenzenes are completely analysed to give the magnitudes and signs of all the ¹H and ¹⁹F coupling constants. The signs of these couplings agree with previous results. The HH and para-HF couplings in these molecules vary linearly with the electronegativity of the substituent in the same way as HH couplings in monosubstituted benzenes. This demonstrates the dominance of the σ-bond coupling mechanism for these couplings. The meta-HF couplings show a marked dependence on the substituent electronegativity, which is not linear, and the ortho-HF and ortho-FF couplings are suprisingly constant.