Free Radicals by Mass Spectrometry. XLIII. Ionization Potentials and Ionic Heats of Formation for Vinyl, Allyl, and Benzyl Radicals

Using an energy-resolved electron beam, ionization potentials for the following free radicals have been measured: vinyl 8.95 V, allyl 8.07 V, benzyl 7.27 V. For vinyl and allyl ions new measurements of thresholds for dissociative ionization give ΔH f (C 2 H 3 + ) = 266 kcal/mol and ΔH f (C 3 H 5 + ) = 226 kcal/mol, leading to neutral radical heats of formation ΔH f (C 2 H 3 ) = 59.6 kcal/mol and ΔH f (C 3 H 5 ) = 40 kcal/mol. The data for benzyl radical and ion give ΔH f (benzyl cation) = 213 kcal/mol.