59527-24-1Relevant academic research and scientific papers
Evaluation of Addition Rates of Thiyl Radicals to Vinyl Monomers by Flash Photolysis. 3. Polar Effects in Addition Reactions of Substituted Benzenethiyl Radicals
Ito, Osamu,Matsuda, Minoru
, p. 5871 - 5874 (2007/10/02)
Rate constants for addition (k1) of para-substituted benzenethiyl radicals (p-XC6H4S*) to vinyl monomers (CH2=CHY) such as isobutyl vinyl ether and vinyl acetate (nonconjugated monomers) and acrylonitrile (conjugated one) have been determined by means of flash photolysis.The rate constants for the reverse reaction (k-1) and the equilibrium constants (K = k1/k-1) have been estimated in the forms of k-1/k2 and Kk2, respectively, where k2 is the rate constant for the reaction between p-XC6H4SCH2C*HY and oxygen; oxygen was used as a selective radical trap to the carbon-centered radicals.From the linear correlations obtained in the Hammett plots of log k1, log (k-1/k2), and log Kk2 vs. the substituent constants (?+), the reaction constants (ρ+) were estimated for each vinyl monomer.The ρ+ (Kk2) values were invariant with a change in vinyl monomers (ρ+(Kk2) = 1.37).The ρ+(k1) values increase with an increase in the electron densities of the double bonds in vinyl monomers.This suggests that a part of the polar effects in the reactivities is determined by the polar effect in the thermodynamic stabilities of the p-XC6H4S* and that another part of the polar effects is caused by the polar resonance structures in the transition state of which contribution varies with the electron-donating or -withdrawing ability of vinyl monomers.
