Laser‐induced kinetics: Arrhenius parameters for t‐C₄H₉ + XI → i‐C₄H₉X + I (X = H,D) and the Heat of Formation of the t‐butyl radical

The metathesis reaction of DI with t ‐C 4 H 9 generated by 351‐nm photolysis of 2,2′‐azoisopropane was studied in a low‐pressure reactor (VLPϕ Knudsen cell) in the temperature range of 302–411 K. The data obeyed the following Arrhenius relation when combined with recent data by Rossi and Golden gathered by the same technique ( t ‐C 4 H 9 by thermal decomposition of 2,2′‐azoisobutane): log k 2 D ( M −1 s −1 ) = 9.60 – 1.90/θ, where θ = 2.303 RT kcal/mol for 302 K < T > 722 K. The metathesis reaction of HI with t ‐C 4 H 9 was studied at 301 K and resulted in k 2 H ( M −1 ·s −1 ) = (3.20 ± 0.62) × 10 8 . An analogous Arrhenius relation was calculated for the protiated system if the small primary isotope effect k 2 H / k 2 D was assumed to be √2 at 700 K. It was of the following form: log k 2 H ( M −1 ·s −1 ) = 9.73 – 1.68/θ. Preliminary data of Bracey and Walsh indicate that earlier Arrhenius parameters determined for the reverse reaction are somewhat in error. Their value of log k 1 ( M −1 ·s −1 ) = 11.5 – 23.8/θ yields 7delta; H f ,300 0 ( t ‐butyl) = 9.2 kcal/mol and S 300 0 ( t ‐butyl) = 74.2 cal/mol7°K when taken in conjuction with this study.