Evidence for the ST-nucleophile mechanism under thermal conditions

5 Evidence for the ST -nucleophile mechanism under thermal conditions 

As already mentioned in Section 1, the radical ion-mediated mechanism, often to be denoted as inverted spin trapping in the following, was discussed and experimentally supported in several isolated cases in the period between 1975 and 1990, but was not subjected to systematic study. In addition, numerous studies were performed on systems which, in the light of later developments, must have involved inverted spin trapping, but which were interpreted differently. Two particularly interesting cases involve the formation of fluoro and acetoxy spin adducts. 

However, since it can be shown that fluoride ion also can participate in the addition-oxidation mechanism (p. 130), at least in media of low dielectric constant (Eberson, 1994), the latter possibility also cannot be excluded on the basis of existing information. Thus, the fluorine dogma makes fluoride ion a key species for mechanistic study (Eberson and Persson, 1997). 

Another mechanistically useful nucleophile is acetate ion and related carboxylates. Acetate ion is difficult to oxidize (Eberson, 1963) and reacts with radical cations in a bond-forming reaction (Eberson and Nyberg, 1976). The oxidation product, the acetoxyl radical, has properties which make trapping it very unlikely in that its decarboxylation rate constant is 1.3 X 109 s 1 (Hillborn 

On the other hand, in l,l,l,3,3,3-hexafluoropropan-2-ol, a solvent with even stronger ability to solvate anions than water and therefore of great usefulness for spin trapping studies (see below), E° values will presumably be higher than in water. 

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