Polar Effects in Addition Reactions of Benzenethiyl Radicals to Substituted Styrenes and α-Methylstyrenes Determined by Flash Photolysis

Article abstract of DOI:10.1021/ja00370a042

The absolute rate constants for the addition reactions of the benzenethiyl radical and its para-chloro derivative to para- and meta-substituted styrenes and α-methylstyrenes have been determined by the flash photolysis technique.The rate constants in the range of ca. 10⁷-10⁸ M^-1 s^-1 have been obtained.From the linear relationships in the Hammett plots vs. ?⁺, the reaction constants (ρ⁺) of C6H5S^. toward substituted styrenes and α-methylstyrenes were estimated to be -0.26 and -0.30, respectively.The latter ρ⁺ value is compatible with the value estimated from the relative reactivities (-0.38).The polar effects of p-ClC6H4S^. toward styrenes (ρ⁺ = -0.56) and α-methylstyrenes (ρ⁺ = -0.63) are larger that those of C6H4S^..The sign and magnitudes of these ρ⁺ values are rationally interpreted in terms of the contribution of such polar resonance structure as -, CH2=C(R)C6H4Y^+.> to the transition state.