Rate constants for formation of semiquinones

Quinones are electron attracting type of molecules and can be reduced by a large variety of reducing radicals. Typically, rate constants for formation of semiquinones due to reactions with eaq (or, Csoiv ) are virtually diffusion-controlled and fall around (1-3) x lO dm mol s (see Table 2). These rate constants are normally directly calculated from a AA versus t plot at 720 nm, representing decay of e, and correcting for the matrix. Alternatively, 

Formation rate constants of transients formed by one-electron reduction of some 

Formation rate constants of transients formed by one-electron reduction of some representative quinones (k in 10 dm mol s ).  

In de-oxygenated aqueous solutions, a semiquinone normally undergoes a bimolecular disproportionation reaction, forming the parent quinone and the correspondii two- electron reduced hydroquinone. 

Typical rate constants fell in the range of 10 -10 dm mol s. However, in cases where substituents are present, an equilibrium of the type of reaction (23) has been observed over a range of intermediate pH values. 

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