The absolute rate constant for the metathesis t-C4H9• + DI → C4H9D + I• and the heat of formation of the t-butyl radical

The Arrhenius parameters for the title reaction have been measured in a very-low-pressure pyrolysis apparatus in the temperature range 644–722 K and are given by log k₂ (M^?1 · sec^?1) = 9.68 - 2.12/θ, where θ = 2.303RT in kcal/mol. Together with the published Arrhenius parameters for the reverse reaction from iodination studies, they result in a standard heat of formation of the t-butyl radical of 8.4 kcal/mol, accepting S⁰(C₄H₉·) = 72.2 e.u. at 300 K from other kinetic data, and thus confirm the accepted value for ΔH_f⁰(t-C₄H₉·), at variance with recent investigations which yielded significantly higher values. This value for ΔH_f⁰(t-C₄H₉·) results in a bond-dissociation energy (BDE) for isobutane of 92.7 kcal/mol.