Effect of oxygen on the EPR spectra of solutions of the stable DPPH radical

Mechanistic Studies on Garratt–Braverman Cyclization: The Diradical–Cycloaddition Puzzle

“…For the sulfones 13 and 2b , we did observe nice stable EPR signals at room temperature (spectrum shown in parts A and B, respectively, of Figure ) with an isotropic g value of 2.004. The g value was found to be close to that for TEMPO ( g = 2.00036) and is thus surely an indication for the generation and presence of organic free radical in cases involving sulfones. − This was also tested by a quenching experiment with molecular O 2 in the triplet ground state. Thus, the EPR signal disappeared when the spectrum was recorded while the reaction mixture was being purged with O 2 gas for 2–4 min (Figure C).…”