The origin of aromatic solvent‐induced shifts in 19F n.m.r.

Aromatic solvent-induced shifts (ASIS) in 19F n.m.r. spectra of several organic fluoro compounds have been determined in several solvents. 19F n.m.r. signals of unsaturated fluoro compounds in C6F6 and C6H6 show excess high field shifts corresponding to the term σc (solvent shift caused by chemical interactions). The mechanism of this shift is discussed in connection with the presence of an F-π interaction. A thermal study also supports this idea.