Electronic structure calculations at the CBS-QB3 level have been performed to compare the rate constants for hydrogen abstractions reactions of allyl and methyl radicals with a series of olefins and dienes. Generally, the rate constants for allyl abstraction are lower than the methyl abstraction by one to two orders of magnitude, due to the higher barriers related to the differences in reaction enthalpies. The calculated results for methyl and allyl abstracting from a wide range of olefins allowed development of a series of rate rules applicable to analogous reactions involving larger resonantly-stabilized free radicals and olefin molecules where such calculations are not feasible. Comparison of the calculated allyl abstractions from olefins to earlier literature estimates suggests that these reactions are significantly faster at higher temperatures than earlier estimates. This could lead to a faster redistribution of resonantly stabilized radicals, thereby potentially influencing the kinetics of the various molecular weight growth pathways.

Predictions of rate constants for hydrogen abstraction reactions by resonantly-stabilized free radicals

248th National Meeting (2014)

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