The fluorine chemical shifts and spin-spin coupling constants of 65 pentafluorophenyl derivatives with widely varying organic substituents were examined. Useful correlations of the three meta coupling constants with the chemical shifts of thepara fluorine were found. It is suggested that these relationships be extended to all compounds of the type considered in order to determine the signs and approximate values of meta coupling constants.Equations for correlation of the fluorine chemical shifts with the Taft constants are presented. The possibility of calculating the Taft constants from the 19F NMR spectra of pentafluorophenyl compounds is being discussed. I N T R O D U C T I O N