Absolute Rate Constants for Radical Additions to Alkenes in Solution. The Synergistic Effect of Perfluorination on the Reactivities of n-Alkyl Radicals1

Laser flash photolysis has been used to determine the absolute rate constants for addition of several partially fluorinated n-alkyl radicals to three styrenes at 25 °C in Freon 113. Fluorination at the γ-position (RCF2CH2CH2 •) gives radicals with essentially the same reactivity as non-fluorinated n-alkyls. The RCH2CF2CH2 • and RCH2CH2CHF• radicals are both about three times as reactive as RCF2CH2CH2 •, but the RCH2CH2CF2 • radical is ca. five to six times rather than ca. three times as reactive as RCH2CH2CHF•. Similarly, the perfluorinated radical CF3CF2CF2 • is much more reactive than would be expected on the basis of the reactivities of the RCH2CF2CH2 • and RCH2CH2CF2 • radicals. Thus, perfluorinated n-alkyl radicals are very considerably more reactive than would be predicted from the individual effects of α-, β-, and γ-fluorination.