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 reactions Of C2F5., n-C3F7., n-C7F15., and n-C8F17. by time-resolved (laser flash photolysis) and competition kinetics. The last three of these radicals exhibit essentially equal reactivities, but C2F5. is somewhat more reactive. The strongly electrophilic nature of these radicals is illustrated by an outstanding Hammett correlation for the addition of 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 significantly, by a respectable correlation, [r] = 0.97, of log k(add) with the ionization 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=CHCN (IP = 10.91 eV) to 7.9 x 10(7) to 8.9 X 10(7) M-1 s-1 for alpha-methylstyrene (IP = 8.19 eV). The n-C8F17. radical is 100 times as reactive in hydrogen atom abstraction from tri-n-butyltin hydride as an n-alkyl radical, with k(abs)H (n-C7F15.) = 2.0 X 10(8) M-1 s-1.