The Role of Fluorine Substituted Acetic Acid in Stabilization of Organosulfur Cation Radicals: A Kinetic E. S. R. Study

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Abstract
Trifluoroacetic acid, the widely used solvolytic agent, is generally acknowledged to be a good solvent in stabilizing organic cations due to its acidity and low nucleophilicity1. Although some years ago Dannenberg2 has carried out INDO calculations on the potential surfaces of such probable interactions between the CF3 group and the carbenium ion, little experimental evidence of the actual molecular interactions has been known. In our continuing study of the CIDEP (chemically induced dynamic electron polarization) applications to chemistry, we have recently initiated a model charge transfer reaction between benzoquinone cation radical and organosulfur compounds in trifluoroacetic acid3. Photochemically induced electron polarization of the benzoquinone cation radical is followed by a well defined secondary polarization transfer in the charge transfer reaction leading to a polarized organosulfur cation radical. One of the interesting observations is that the organosulfur cation radical polarization is the strongest in trifluoroacetic acid solvent. Since trifluoroacetic acid is well known to possess the unique ‘property’ of stabilizing cation radicals, we wish to report here some e. s. r. experimental evidence which will shed some light on the nature of the molecular interactions between the fluorine substituted acetic acids and thianthrene cation radicals in solution which is responsible for the stabilization of the radicals as observed by kinetic e.s.r. measurements.