The normal or “triplet” ground state (3Σg–) of molecular oxygen is that of a biradical,· O–O·, but “singlet” oxygen (1Δg) OO, which is structurally similar to ethylene, is the initial product of heterolytic decompositions of hydrogen peroxide or of per-acids.“Singlet” oxygen reverts to normal “triplet” oxygen by a bimolecular reaction that produces chemiluminescence but is sufficiently long-lived to be able to react as a dienophil; it combines with anthracenoid ...
