Quantitative aspects of radical addition. Part IV. Rate-constant ratios for addition of trichloromethyl and thiyl radicals to olefins

Abstract

The factors affecting the rate of addition of free radicals to olefinic double bonds have been examined with special reference to the relative importance of polar, resonance, and steric phenomena. A valid competitive method has been employed to measure the relative reactivities of substituted trans-stilbenes, substituted styrenes, and various aliphatic olefins towards thiyl radicals derived from thioglycollic acid and its methyl ester, and trichloromethyl radicals from bromotrichloromethane. In a number of experiments both the unchanged olefins and the 1 : 1 adducts were estimated, thus accounting, for the first time, for all the olefin in the system. The results, while confirming the electrophilic character of the radicals studied, indicate that no single factor is entirely responsible for the variations in olefin reactivity. The absence of significant polar contributions to the transition state in the addition of thiyl radicals to substituted α-methylstyrenes has been established.The orientation of the addition of thiyl radicals to a number of substituted styrenes and aliphatic olefins has been established and radical addition to C-(2) of hept-1-ene and oct-1-ene has been observed for the first time.