The azoethane‐initiated thermal reaction of isobutene. Heat of formation of the 2‐methyl‐2‐pentyl radical

The azoethane‐sensitized thermal reaction of isobutene has been studied at 526–565 K. The initial concentrations of azoethane and isobutene were in the ranges of 1.40–10.5 × 10 −4 and 6.78–26.6 × 10 −4 mol/dm 3 , respectively. From the initial rates of formation of ethane and 2‐methylpentane the heat of formation of the 2‐methyl‐2‐pentyl radical was determined. The result obtained is ± H   f 0 (2‐methyl‐2‐pentyl) = 0.8 ± 2.0 kcal/mol. The entropy of the radical, obtained from statistical mechanical calculations and experimentally, is S 0 (2‐methyl‐2 pentyl) = 92.8 ± 1.5 cal/mol°K. The results support the high heat of formation of the t ‐butyl radical suggested by different authors.