ABSOLUTE RATE CONSTANTS FOR SOME REACTIONS OF PERFLUORO-N-ALKYL RADICALS IN SOLUTION

Absolute rate constants have been measured at 298 +/- 2 K for some rea ctions Of C2F5., n-C3F7., n-C7F15., and n-C8F17. by time-resolved (las er flash photolysis) and competition kinetics. The last three of these radicals exhibit essentially equal reactivities, but C2F5. is somewha t more reactive. The strongly electrophilic nature of these radicals i s illustrated by an outstanding Hammett correlation for the addition o f n-C8F17. to four para-substituted styrenes, log(k(add)X/k(add)H) = - 0.53sigma, [r] = 0.99 (X = p-CH3O to p-CF3), and, far more significant ly, by a respectable correlation, [r] = 0.97, of log k(add) with the i onization potentials (IP) of 13 terminal olefins, the values of k(add) for n-C3F7. ranging from 1.6 X 10(6) to 2.2 X 10(6) M-1 s-1 for CH2=C HCN (IP = 10.91 eV) to 7.9 x 10(7) to 8.9 X 10(7) M-1 s-1 for alpha-me thylstyrene (IP = 8.19 eV). The n-C8F17. radical is 100 times as react ive in hydrogen atom abstraction from tri-n-butyltin hydride as an n-a lkyl radical, with k(abs)H (n-C7F15.) = 2.0 X 10(8) M-1 s-1.