The absolute rate constant for the metathesis t ‐C 4 H 9 • + DI → C 4 H 9 D + 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 k 2 ( M −1 · sec −1 ) = 9.68 ‐ 2.12/θ, where θ = 2.303 RT 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 S 0 (C 4 H 9 ·) = 72.2 e.u. at 300 K from other kinetic data, and thus confirm the accepted value for Δ H f 0 ( t ‐C 4 H 9 ·), at variance with recent investigations which yielded significantly higher values. This value for Δ H f 0 ( t ‐C 4 H 9 ·) results in a bond‐dissociation energy (BDE) for isobutane of 92.7 kcal/mol.