A 13C{1H} double resonance study of the signs of 1H19F and 13C19F spin coupling constants in fluorobenzenes and 2‐fluoropyridine

Abstract

AbstractThe signs of all 13C19F and 1H–19F coupling constants in fluorobenzene, some substituted derivatives, and in 2‐fluoropyridine have been related using single‐frequency 13C{1H} double resonance techniques. All 13C19F couplings in these compounds are shown to be positive. Direct experimental proof is given for a positive sign for the small five‐bond 1H19F coupling constant (=0.2—0.3 Hz) in fluorobenzene. The positive sign for 4J(C‐4, F) in fluorobenzene is in accord with a positive π‐electron contribution to this coupling.