The relative reactivities of fluorobenzene, all di-, tri-, and tetrafluorobenzenes and pentafluorobenzene toward sec-butyllithium have been assessed in THF at -100 DegC. At this temp. no subsequent transmetalation reactions take place but those compromise the outcome of the competition expts. if the latter are conducted at -75 Deg. The rates detd. at -100 Deg reflect the basicity differences between the naked (oligo)fluorophenyl anions to the extent of 10%. [on SciFinder (R)]