ABSOLUTE RATE CONSTANT FOR THE METATHESIS TERT-C4H9.+DI-]C4H9D+I. AND THE HEAT OF FORMATION OF THE TERT-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 ΔHf0(t‐C4H9·), at variance with recent investigations which yielded significantly higher values. This value for ΔHf0(t‐C4H9·) results in a bond‐dissociation energy (BDE) for isobutane of 92.7 kcal/mol. Copyright © 1979 John Wiley & Sons, Inc.