A mixture of biquinone (QQn) and bihydroquinone (HHn) bearing tert-butyl substituents at 5,5'- (n = 1) and 6,6'-positions (n = 2) yields hydroquinonylquinone (HQn) as an equilibrium product by quinone/hydroquinone exchange. The equilibrium constants for the formation of HQ1 are higher than those of HQ2 in all solvents. While the exchange between QQ1 and HH1 is slow, that between HQ1s occurs so rapidly in CDCl3 that it is observed in phase-sensitive 2D NOESY NMR spectra.