Determination of ΔHf2980(C6F5I,g) from Studies of the Combustion of Iodopentafluorobenzene in Oxygen and Calculation of D(C6F5—X) Bond Dissociation Energies
The heat of formation of iodopentafluorobenzene has been determined using the direct combustion method previously developed and used for hexafluorobenzene and octafluorotoluene. The combustion with oxygen yields CO2, CF4, F2, I2, and IF5. With a tenfold excess of oxygen the average CO2 to CF4 molar ratio is 11.08 ± 0.028. A material balance was obtained for carbon and fluorine. An apparent shortfall of about 30% in iodine has been related to the formation of IO2(OH) during analysis. The value of ΔHf2980 (C6F5I,g) = −133.2 ± 3.0 kcal mol−1 has been combined with D(C6F5—I) and ΔHf2980(I, g) to obtain ΔHf2980(C6F5,g) = −92.6 kcal mol−1 Using this value and the appropriate values of ΔHf2980 (C6F5X,g) and ΔHf2980(X, g), values of D(C6F5—X) have been calculated for X = OH, H, F, Cl, I, CH3, and CF3.