Kinetic parameters of alkyl, alkoxy, and peroxy radical isomerization

The activation energies and rate constants that specify each class of these reactions are calculated. Alkyl radical isomerization is characterized by the following activation energies of a thermally neutral reaction depending on the cycle size in the transition state (n is the number of atoms in a cycle): E-e,E-0 (kJ/mol) = 46.6 (n = 6), 59.4 (n = 5), and 57.1 (n = 7). Alkoxy radicals isomerize with E-e,E-0 (kJ/mol) = 53.4 (n = 6), whereas peroxy radicals isomerize with E-e,E-0 (kJ/mol) = 53.2 (n = 6) and E-e,E-0 (kJ/mol) = 54.8 (n = 7). The E-e,E-0 value varies with changes in the cycle size and the strain energy in cycloparaffin CnH2n in the same manner. The activation energies E-e,E-0 for the intra- and intermolecular H-atom abstractions are compared. It is found that E-e,E-0 (isomerization) < E-e,E-0(R* + (RH)-H-1) for alkyl radicals and that E-e,E-0 (isomerization) approximate to E-e,E-0 (RO* (RO*(2)) + (RH)-H-1) for alkoxy and peroxy radicals.