J. Lusztyk

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.