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. Author manuscript; available in PMC: 2018 Oct 30.
Published in final edited form as: J Am Chem Soc. 2016 Nov 30;138(49):15903–15910. doi: 10.1021/jacs.6b05797

Figure 3.

Figure 3.

Plot of the 2 e–/2 H+ reduction potentials (filled black circles), the sum of the pKa values (filled gray circles), and the average of the two 1 e– reduction potentials (open gray circles) as functions of the sum of the Hammett constants (Σσ) for all substituted quinones in Chart 2. As discussed in the text, intramolecular proton transfer (PT) may occur in the Q•– and Q2– states for the SH, OH, or CO2H substituents, but is not included in the calculated values shown in this figure. This intramolecular PT does not impact the 2 e-/2 H+ reduction potentials but does impact the breakdown into the individual contributions from reductions and external protonations.