The measurement of hammett ρ-values for homolytic reactions by electron spin resonance spectroscopy : reaction of t-butoxyl radicals with substituted anisoles

Abstract

The technique of steady-state e.s.r. spectroscopy has been used for determining the relative reactivity of ring-substituted anisoles towards t-butoxyl radicals at +25, 0, and –30 in C₂Cl₃F₃, at –55 in cyclo-C₃H₆, and at –73 and –94 °C in CFCl₃. The results show a good Hammett ρσ⁺ correlation, where ρ is given by the expression ρ=–156/T(in K), and ρ(45 °C)–0.49. The correlation with σ is less satisfactory, when ρ(45 °C)=–0.52; previous studies by product analysis have given ρσ correlation with ρ–0.41, and the possible origin of this discrepancy is discussed. In 1 : 1 Bu^tOH–C₂Cl₃F₃ as solvent at –11 °C, ρ=–0.74, whereas in C₂Cl₃F₃ alone, ρ=–0.59.