Structure—reactivity relationships in radical interactions

Howard and Ingold [10,69,119] have carefully measured values of 2fet for a variety of R02-. The R02- radicals fall in the following order with respect to increasing values of 2kt f-alkyl acrylic allylic cyclic secondary acrylic benzylic primary. Rate coefficients span a range from 103 to 1081 mole-1 s 1 [10]. 

Substituent effects in R02-, where R is benzyl or substituted benzyl, have only small effects on 2kt, largely unrelated in direction to mesomeric or inductive effects of the substituents ring-substituted styrenes [127] have 2kt = (3.88 1.24) X 1071 mole-1 s 1 a-substituted toluenes have 2kt = (10.3 10.1) X 1071 mole 1 s 1 [128], Among f-R02-, increasing bulk in R leads to higher values for 2kt which range from 1.3 X 1031 mole-1 s 1 for t-butyl to 6 X 104 1 mole 1 s 1 for 1,1-diphenylethyl [129], 

Acylperoxy radicals arising from the oxidation of aldehydes apparently terminate via a tetroxide which then cleaves to form, first, primary carbon radicals and second, primary alkylperoxy radicals which terminate rapidly [130,131]. Termination rate coefficients for aliphatic aldehydes have values ranging from 0.7 X 107 to 10 X 1071 mole-1 s-1 [10]. 

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