The nuclear magnetic resonance spectra of fluoroaromatics. Part V. The 13C spectra of some fluorobenzenes and fluorobenzofurans

Abstract

The natural abundance ¹³C spectra of some 1-substituted 2,3-difluorobenzenes and of some 6-substituted 3-ethoxycarbonyl-4,5,7-trifluoro-2-methylbenzofurans have been obtained. The spectra have been assigned by use of ¹H and ¹⁹F decoupling techniques, together with a consideration of the ¹³C substituent chemical shifts, and of ¹³C–¹⁹F coupling constants. Comparison of ¹³C substituent chemical shifts in substituted benzenes and benzofurans suggests that these parameters can be safely transferred from one aromatic system to another. Substituent effects on ¹³C–¹⁹F coupling constants have been evaluated, and the effects of ortho-substituents on ¹J couplings shown to occur via a π-bond mechanism.