Physical Measurements and Calculations

The solubilities in hexafluorobenzene of the gases He, Ne, Ar, Kr, Ng, 0 CO, COj, CH, CFg, CgF, CgFj, and cyclo-CgFg have been determined at 1 atm and 10—25 °C results are compared with similar data for benzene itself and are examined in the light of regular solution theory and semi-empirical calculations. The critical properties and vapour pressure of pentafluorobenzene, chloropentafLuorobenzene, 2,3,4,5,6-pentafluorotoluene, and (limited data owing to decomposition) pentafiuorophenol have been measured and the behaviour of the vapour-pressure curves is discussed.  

The equilibrium acidities per hydrogen atom of pentafluoro- (pK = 25.81 0,16), 1,2,3,4-tetrafluoro- (31.52 0.21), and o-difluorobenzene (34.98 0.19) at 34 °C have been determined by equilibration with caesium cyclo-hexylamide in cyclohexylamine cf. 9-phenylfluorene, pK = 18.49 in this system). Extrapolation to benzene itself gives pJST = 43.0 + 0.2 on the same scale. Analysis of the molar Kerr constants and apparent dipole moments at 25 °C of the compounds p-XCgHi CFa (X = H, F, Cl, or CFg), CgFj-CF, and ff7-C6H4(CX3)a (X = H or F) in carbon tetrachloride has provided the anisotropic electron polarizability for the Cat—CF, group the results are compared with those for Cxr—CX3 (X = H, Me, or Cl) for evidence of hyperconjugation.  

and p-FC,H4Me, o- and m-FC,HiCF PhF, - CeFe, and C,F6H has been studied, and trends in the radiative and non-radiative decay rates of the excited molecules are discussed. - c/s-But-2-ene is effective in increasing the fluorescent and triplet yields of pentafluorobenzene. The decay rate of triplet benzophenone, produced by laser flash photolysis, is ca. ten times faster in hexafluorobenzene than in benzene, and reversible addition of the triplet species to the aromatic ring may play an important role. The phosphorescence spectrum of decafluoro-benzophenone has been studied, and the triplet state of this ketone (see also p. 380) in inert solvents e.g. perfluoromethylcyclohexane) has a lifetime of 20 ps. U.v. irradiation of decafluorobenzophenone in isopropyl alcohol 

Jonasson, F. C. Sopchyshyn, and F. P. Sargent, presented at the 23rd International Congress of Pure and Applied Chemistry, Boston, Mass., July 25-30, 1971 (quoted in ref. 131). 

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Although it is possible to predict the result from physical measurements and calculations, the patterns are well established experimentally for most heterocyclic systems. These general selectivity patterns for... 

Physical Measurements and Calculations. —Reaction Kinetics and Rate Theory. The reactions of fluorinated benzenes (PhF, 1,2- and l,4-FaC6H4, lA3,4-F4C6Ha, CaFsH, and CeFe) with hydrated electrons and hydroxyl radicals In aqueous solution have been investigated by pulse radiolysis and y-irradiation experiments. Electron capture by the highly fluorinated compounds usually leads to loss of fluoride e.g. CeFe + eaq - CeFe -H F ), but radical anions formed from mono-or di-fluorobenzenes are protonated to give fluorocyclohexadienyl radicals, detected by U.V. spectroscopy fPhF -I- eaq - 7 PhF -> -CeHeF). The reaction of hexafluoro-benzene with hydroxyl radicals probably gives the pentafluorophenoxy radical... 

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