Fluorine magnetic resonance studies. V. Fluorine-fluorine coupling in 1,4-difluorobenzenes

Abstract

A number of substituted 1,4-difluorobenzenes were examined by 19F n.m.r. spectroscopy and 5JFF was found to vary with the nature of the substituent in much the same way that it does in more heavily substituted difluorobenzenes. Only in 2',5'-difluoroacetophenone is 5JFF larger than it is for 1,4-difluorobenzene itself. The magnitude of 5JFF is increased when a small ring is fused to the benzene ring, i.e. in 4,7-difluorodihydroindenes and 2,5-difluorobicyclo[4,2,0]octa-1,3,5- trienes. Similar effects have been reported for 5JHH in aromatic systems, and the value of 5JHH for tricyclo-[6,2,0,03,6]deca-1,3(6),7-triene is found to be 1.61 Hz.