INVERTED SPIN-TRAPPING .3. FURTHER-STUDIES ON THE CHEMICAL AND PHOTOCHEMICAL OXIDATION OF SPIN TRAPS IN THE PRESENCE OF NUCLEOPHILES

Inverted spin trapping, denoting the reaction between the radical cation of a spin trap (ST.+) and a nucleophile (Nu(-)), has been further explored with respect to the photochemical generation of ST.+ and the use of 5.5-dimethyl-1-pyrroline 1-oxidet (DMPO) and 3.3,5.5-tetramethyl-1-pyrroline 1-oxide double dagger (TMPO) as ST. it is shown that photoexcitation of N-benzylidene-tert-butylamine N-oxide (PBN) in the presence of a weak electron acceptor, tetrabutylammonium 12-tungstocobaltate(lII), and a nucleophile gives the corresponding spin adducts, PBN-Nu(.), most likely via the intermediate radical cation PBN.+. This species could also be generated by sensitized photoxidation and made to react with Nu(-). The cyclic N-oxides DMPO and TMPO are more difficult to oxidize than PBN (by 0.2-0.3 V). They both engage in inverted spin trapping, using both thermal and photochemical oxidation, but in a more restricted way than for PBN.