Quinones, Semiquinones, and Catechols

Quinones, Semiquinones, and Catechols. All molecules with unsaturated bonds (olefins, acetylenes, aromatics, carbonyls, quinones, etc.) have a degree of electrophilicity and electron affinity. Within a class, the extent of conjugation 

5-DTBSQ) in the presence of an equivalent of HO-.12 The first reduction step is a reversible one-electron process that is followed by a second one-electron reduction, which can be reversible in rigorously anhydrous media to give catechol dianion (3,5-DTBC2-)  

Although DTBC2- is a strong base that is hydrolyzed by residual H20 

In many cases, the second reduction step of quinones [Eq. (12.10)] is irreversible and due to the facilitated reduction of residual H20  

In the presence of hydronium ions (H30+), the reduction of the quinones is an irreversible two-electron process (ECEC), in which the first step is the more difficult (requiring the more negative potential). 

---

The quinone, semiquinone, and catecholate species particularly of iron are important in electron-transfer processes in photosynthesis and respiration. 

Redox active dioxolene derivatives exist as different isomers of benzo-quinone, semiquinonate and catecholate by two-step one-electron transfer (Scheme 55). A linear chain structure with direct a Rh Rh bond was reported with 3,6-di-tert-butyl-l,2- benzosemiquinonate (3,6-DBSQ) radical anion in [Rh (C0)2(3,6-DBSQ)]. It was originally synthesized by the reaction of T1(3,6-DBSQ)... 

---