The kinetics of the reactions of pentafluoropyridine with potassium aroxides, leading to formation of polyfluorinated aryl pyridyl ethers, conform to the Bro/nsted equation. The data obtained for potassium pentafluorophenoxide deviate from the general correlation because of readily occuring reverse reaction, replacement of the pentafluorophenoxy group by released fluoride ion. PM3 calculations of the electronic structure of the reagents, intermediate σ-complexes, and products showed that the replacement of fluorine in pentafluoropyridine is a charge-controlled process, whereas unusually easy replacement of the pentafluorophenoxy group in the corresponding aryl pyridyl ether by fluorine is explained by structural features of its lowest unoccupied molecular orbital.