Arrhenius parameters for the alkoxy radical decomposition reactions

Arrhenius parameters for the decomposition reactions of various alkoxy radicals are evaluated. The recommended values for tert ‐butoxy radical decomposition reaction are log A (s −1 ) = 14.1, E a = 15.3 kcal/mol. magnified image The parameters give reasonably self‐consistent results with related rate constants, product distributions of hydrocarbon oxidation reactions, and the values reported in different laboratories in different environments. A reworking of data by Batt et al. on RO + NO and RO + NO 2 leads to a lowering of his A factors for these reactions by a factor of 5. It also leads to a similar lowering of the A factors for RO decompositions. The intrinsic activation energies E for the addition of alkyl radicals R to the carbonyl group are not only found to be a function of the exothermicity of reaction, but they are also dependent on the nucleophilicity of the alkyl radicals. For each radical R (Me, Et, i ‐Pr) the data can be fit to an Evans–Polanyi plot E = a + b (δ H ), where a uniform slope b = 0.58 can be found for all R. The intercepts a are then found to decrease nearly linearly with the decreasing ionization potential of R, namely, a = 2.1 [IP] – 6.2 (kcal/mol), with the ionization potential given in electron volts.