C6F5X Bond Dissociation Energies: Determination from Appearance Potential Measurements and Correlation with Thermochemical Data

Abstract

Appearance potentials for C6F5+ from C6F5X (X = F, Cl, Br, I) have been determined relative to argon (15.76 eV) by the extrapolated voltage difference method. The respective appearance potential values are 16.86, 15.85, 14.93, and 13.21 eV with an estimated precision of ± 0.05 eV. Combining differences in these values with the kinetic values of D[C6F5—I] = 66.2 kcal mol−1 leads to D[C6F5&([a-z]+);F] = 150.4 ± 2.0 kcal mol−1, D[C6F5&([a-z]+);Cl] = 127.1 &([a-z]+); 2.0 kcal mol−1, and D[C6F&([a-z]+);Br] = 105.9 ± 2.0 kcal mol−1Comparison with D[C6F5—X] (X = F, Cl, I) from thermochemistry (1) indicates that the combined excitation energies, kinetic energies, and chemical shifts for the process C6F5X → C6F5+ + X are constant within experimental error.