Reaction of n-propyl radicals with oxygen, hydrogen and deuterium

Abstract

n-C₃H₇ radicals have been produced by the oxidation of n-C₃H₇CHO at 450°C. By measuring the relative yield of C₃H₆ and C₃H₈, a value for the ratio k₄/k₁= 0.040 ± 0.005 has been obtained. A value of k₄ can be obtained, based on the value of 2.9 × 10¹⁰ l. mol^–1 s^–1 assumed for the combination of two C₃H₇ radicals, which gives k₁= 3.1 × 10⁷ at 450°C. By measuring the increased yield of C₃H₈(or C₃H₇D) in the presence of H₂(or D₂), the ratios k₁/k₂= 347 ± 10, k₂/k₃= 2.3 ± 0.2 at 450°C are obtained. n-C₃H₇+ O₂→ C₃H₆+ HO₂(1), n-C₃H₇+ H₂→ C₃H₈+ H (2), n-C₃H₇+ D₂→ C₃H₇D + D (3), n-C₃H₇+ C₃H₇CHO → C₃H₈+ C₃H₇CO. (4)

The value for k₂/k₃ suggests that E₃–E₂= 0.7 kcal mol^–1 which indicates a lowering of the zero-point energy in the transition state by about 1.1 kcal mol^–1 when H₂ is replaced by D₂. Using entropy data, and the Arrhenius parameters for reaction (– 2), A₂= 2.6 × 10⁹ and E₂= 14.8 kcal mol^–1.