Kinetics of gas-phase addition reactions of methyl radicals. I. Addition to ethylene,acetylene, and benzene

The reactions have been studied by a mass-balance method involving the photolysis of small amounts of biacetyl in the presence of a large excess of isobutane containing a small proportion of the unsaturated substrate. The following Arrhenius parameters have been derived:

			Temperature
	E	log A	range
Reaction	(kcal/mol)	(1./mol·sec)	(°K)
?H3 + C2H4 → ?3H7	7.3 ± 1.0	8.32 ± 0.5	350 – 500
?H3 + C2H2 → ?3H5	7.7 ± 1.5	8.79 ± 0.8	379 – 487
?H3 + C6H6 → C7H9	7.6 ± 1.0	8.79 ± 0.5	372 – 484

The results for methyl addition to ethylene are based on previous determinations by other techniques as well as the present studies. The results for methyl addition to acetylene and benzene are derived solely from the present experiments and are calculated relative to a rate constant of log k₂(l./mol·sec) = 7.42 - (7.1/θ) for the reference reaction (2), ·H₃ + (CH₃)₃CH → CH₄ + ·₄H₉.