Temperature Dependence of Disproportionation–Combination Ratios for Alkyl Radicals in Liquid Methane
Abstract
The ratios of rate constants for disproportionation to combination have been measured for ethyl radicals and for i-propyl radicals in liquid methane between −181 and −94 °C. The radicals were generated by γ-radiolysis of dilute methane solutions of ethylene-d 4 or propylene-d 6 . The activation energy for combination was found to exceed that for disproportionation by 290 ± 30 cal mol −1 for ethyl radicals and by 255 ± 25 cal mol −1 for i-propyl radicals. In both cases the disproportionation—combination ratio in the liquid, extrapolated to room temperature, is greater than that in the gas phase by a factor of about 2.5. These results are interpreted as indicating that disproportionation and combination reactions proceed by way of different transition states.
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