Structure-reactivity relationships in radical reactions: A novel method for the simultaneous determination of absolute rate constants and structural features

Analysis of the ESR line width in time-resolved (TR-ESR) experiments is sho wn to be a suitable tool for the measurement of addition constants of phosp hinoyl and substituted benzoyl radicals. Compared with kinetic investigatio ns, which make use of the resonance intensity or integral, observation of t he line width as a function of monomer concentration has the advantage that the experimental parameter is not affected by spin-polarization processes and, therefore, a lengthy determination of these polarization parameters is avoided. The resulting addition constants are discussed with respect to th e experimental hyperfine coupling constants and the geometry of the radical s. TR-ESR experiments simultaneously provide rate constants and ESR paramet ers and allow structure-reactivity relationships to be established.