Long-range proton-fluorine spin-spin coupling and ¹⁹F substituent chemical shifts (SCS) in the naphthalene ring system

Abstract

A number of acetyl-substituted fluoronaphthalenes have been synthesized and their fluorine as well as proton N.M.R. spectra have been measured. The methyl proton resonances of these derivatives appeared as a doublet which indicated long-range coupling with the fluorine. It was observed that the coupling (J_Me,F) for 3-acetyl-2-fluoronaphthalene and o- fluoroacetophenone is independent of the magnitude of the ¹⁹F substituent chemical shifts (scs) which are shown to be sensitive indices of the bond-order differences in naphthalene (C 1 and C 2; C 2 and C 3) and benzene. Furthermore, the magnitude of the long-range proton-fluorine spin-spin coupling constants are solvent dependent. The data are clearly in accord with a predominant contribution of a ?direct? mechanism to the proton-fluorine spin-spin coupling.