Arrhenius parameters for the alkoxy radical decomposition reactions

Abstract

Arrhenius parameters for the decomposition reactions of various alkoxy radicals are eval-The recommended values for tert -butoxy radical decomposition reaction are uated. log A (s-l) = 14.1, E, = 15.3 kcal/mol.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 + NO2 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 ( A f f ) , 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.

Rate coefficients and mechanisms of the reaction of cl‐atoms with a series of unsaturated hydrocarbons under atmospheric conditions

“…The decompositions of the ␤-chlorinated species are characterized by somewhat lower H values (3-5 kcal mol −1 ) than for the corresponding unsubstituted radical decompositions [54,56,57], which leads to only a modest reduction in the corresponding activation energies (0-2 kcal mol −1 ). It has been shown [48,58] that the activation energy (E a ) for a series of alkoxy radical decompositions involving a common leaving group is related to the where IP refers to the ionization potential of the (common) leaving group in eV, and E a and H d are in kcal mol −1 . Consideration of the data in Table II reveals that, in this context, ␤-chlorinated alkyl radicals are slightly poorer leaving groups than CH 3 radicals (higher activation energy for a given endothermicity), despite the fact that the ionization potential for CH 2 Cl (8.9 eV [59]) is somewhat lower than that of the CH 3 radical (9.8 eV [59]).…”

High‐temperature shock tube study of the reactions CH3 + OH → products and CH3OH + Ar → products

“…In addition, reactions describing azomethane decomposition [19] and TBHP chemistry [11,16,17] were added to the mechanism. Table I presents these and other reactions that are important in the CH 3 + OH experiments.…”

Direct measurements of the reaction OH + CH2O → HCO + H2O at high temperatures

“…Acetone chemistry, which is not a part of the GRI Mech 3.0 model, was incorporated into the mechanism from the detailed LLNL hydrocarbon oxidation model (a total of 23 reactions involving CH 3 COCH 3 , CH 3 COCH 2 , and CH 3 CO were added) [20]. The TBHP decomposition pathways, reactions (5) and (6), were also added to the model; rate coefficients suggested by Benson [15,16] were used for these reactions. As for the decomposition of 1,3,5-trioxane, the rate expression of Irdam and Kiefer [21] was used.…”