Photobromination of C2H5Cl in the Presence of C2H6. The Heat of Formation of the CH3CHCl Radical and the D0 (CH3CHCl-H) Bond Dissociation Energy

Article abstract of DOI:10.1021/j100287a041

The gas-phase photobromination of C2H5Cl in the presence of ethane as competitor has been studied between 32 and 95 deg C at total reactant pressures of ca. 32 Torr and sevenfold hydrocarbon excess over bromine.Under these conditions hydrogen abstraction by bromine atoms from C2H5Cl occurs almost exclusively from the CH2Cl group.Over the temperature range stated, the relative rate constants conform to an Arrhenius rate law, which combined with the known rate parameters for ethane, log (A/cm³ mol^-1 s^-1) = 14.135 +/- 0.056, E = 13.66 +/- 0.14 kcal mol^-1, yield for the abstraction of secondary hydrogen in CH3CH2Cl k₁/cm³ mol^-1 s^-1 = 1E12.182+/-0.091 exp<-(9.14 +/- 0.16 kcal mol^-1)/RT>.From an analysis of kinetic and thermochemical data on these and related compounds in the literature the following radical heats of formation and C-H bond dissociation energies are deduced: ΔH_f⁰(CH3CHCl) = 16.75 +/- 1.0; D⁰(CH3CHCl) = 1.0; ΔH_f⁰(CH3CHF) = -17.7 +/- 1.1; and D₀(CH3CHF-H) = 97.3 +/- 1.1 kcal mol^-1.