Thermodynamic properties of fluorine compounds 9. Enthalpies of formation of some compounds containing the pentafluorophenyl group

Abstract

The energies of combustion of pentafluorobenzene, methylpentafluorobenzene, pentafluorophenol, and chloropentafluorobenzene have been determined using a rotating-bomb calorimeter. The sublimation pressures at temperatures near 25 °C of p-fluorobenzoic acid, pentafluorobenzoic acid, and pentafluorophenol have been measured by a transpiration method, and enthalpies of sublimation have been calculated from the results of these measurements. Enthalpies of formation in the gas state at 298 K (derived from these and previously published results) are reported for pentafluorobenzene, methylpentafluorobenzene, pentafluorophenol, chloropentafluorobenzene, and pentafluorobenzoic acid, together with a slightly revised value for hexafluorobenzene, and are discussed in terms of electrostatic interaction between the dipolar substituents of the benzene nucleus.