The reactivity of a number of aryl fluoride monomers used in nucleophilic aromatic substitution polymerization was explored utilizing F-19 NMR experiments. NMR is a valuable tool for evaluating the electron-withdrawing effect of substituents present on phenyl rings. When an electron-withdrawing group is present on a phenyl ring, a partial positive charge develops at the ortho and para positions through resonance interactions. While both C-13 and F-19 NMR were used to probe the electron density at the actual site of nucleophilic reaction, F-19 NMR chemical shifts proved to be the most sensitive probe with a chemical shift range spanning 2500 Hz between the most activated monomer examined, difluorodiphenyl sulfone, and nonactivated fluorobenzene. The F-19 shifts reflect the reactivity of the individual monomers examined. Taft inductive and resonance parameters were calculated for a series of monomers from F-19 data and used to identify activating forces for the monomers. NMR data were compared with calculated net atomic charges. Relative reactivity studies were also performed in order to verify the utility of this fast and convenient NMR probe of monomer reactivity.