Absolute Rate Constants for Radical Additions to Alkenes in Solution. The Synergistic Effect of Perfluorination on...

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.