Semidione

Semidiones are radical anions analogous to semiquinones, obtained from the one-electron reduction of non-quinone conjugated dicarbonyls.

[1] The simplest possible semidiones are derived from 1,2-dicarbonyls and have structure R−C(−O−)=C(−O•)−R' ↔ R−C(−O•)=C(−O−)−R', making them the second member of a homologous series starting with ketyl radicals and continuing with semitriones.

[1] They are often transient intermediates, appearing in reactions such as the final reduction step of the acyloin condensation.

[2] Benzil semidione (Ph−C(−O−)=C(−O•)−Ph ↔ Ph−C(−O•)=C(−O−)−Ph), synthesized by Auguste Laurent in 1836, is believed to have been the first radical ion ever characterized.

[3]: 425 [4] Semidehydroascorbate is a relatively stable semitrione produced by hydrogen abstraction from ascorbate (Vitamin C).