Heat of Formation of the tert-Butyl Radical

Calculations using a variety of high-level theoretical procedures predict a heat of formation (ΔH°_f 298) for the tert-butyl radical of 57 ± 7 kJ mol^-1, which is slightly higher than recent experimental recommendations (51.5 ± 1.7 and 51.8 ± 1.3 kJ mol^-1). The heats of formation for the tert-butyl cation (716 ± 10 kJ mol^-1) and isobutene (−14 ± 8 kJ mol^-1) predicted by the same theoretical methods are also slightly higher than the experimental values (711.5 ± 0.2 and −16.9 ± 0.9 kJ mol^-1, respectively), while the proton affinity of isobutene (802 ± 4 kJ mol^-1) is in very good agreement with experiment (801.7 ± 1.4 kJ mol^-1). On the other hand, the calculated ionization energy of the tert-butyl radical (6.81 ± 0.06 eV) is significantly higher than two experimental values (6.58 and 6.70 eV), suggesting that a reexamination may be desirable.