DETERMINATION OF UNIMOLECULAR RATE DATA FROM REACTION MIDPOINT TEMPERATURES DERIVED FROM EPR-SPECTRA

The activation energies of unimolecular homolytic reactions (E-r) are predicted to correlate linearly with the mid-point temperatures (T-mil d) defined as the temperature at which the rearranged and unrearranged species are of equal concentration, for photochemically initiated pro cesses under EPR conditions. A linear relationship (E-r/kcal mol(-1) = 0.044T(mid) + 0.22) has been demonstrated from experimental data and shown to hold for a range of solvents and instrumental configurations. The relationship will facilitate the determination of kinetic paramet ers, particularly for processes where the spectra of the intermediates are of low intensity.