Reactivities of cis ‐ and trans ‐buten‐2‐yl free radicals in presence of D 2 S. II. Absolute values of rate constants and isotopic effects

Cis ‐ and trans ‐buten‐2‐yl free radicals are shown to react with butene‐2 cis (B c ) and D 2 S in the following metathetical steps:giving rise to butenes‐1 (B 1 ). The initial formations of butene‐1,3 d 1 and total butene‐1 in D 2 SB c mixtures have been studied in the initial pressure range 20–200 torr for B c , 0–41 torr for D 2 S and at 717–817 K. The main initiation and termination steps are shown to be:Assuming a rapid equilibrium between cis ‐ and trans ‐C 4 H 7⋅ , k i ≃ 10 15.5 exp(−85.5/ RT ) s −1 ( RT in kcal mol −1 ) and k t ≃ 10 13 mol −1 cm 3 s −1 , we get: k 2 c ′ = 1.1 k 2 t ′ = 10 12.0 exp[(−9.25 ± 2)/ RT ] mol −1 cm 3 s −1 and k 2 + 1.5 k 2′ ≃ 10 12.1 exp[(−15.2 ± 2)/ RT ] mol −1 cm 3 s −1 . Isotopic effects relating to processes (2c′) + (2t′) and to (i′) have been evaluated.