Table 2.

Experimental pK_a values determined by spectrophotometry,^a anodic peak potentials (E_pa) determined at the pK_a by differential pulse voltammetry,^b and rate constants for reactions with peroxyl radicals (k_inh) determined by inhibited autoxidation of styrene^c

	pKa	Epa @ pKa (V)	kinh (M−1 s−1)
1	9.78	0.32	0.5 × 106
2	8.28	0.48	0.4 × 105
3	5.89	1.02	1.0 × 104
5a	9.27	0.12	4.8 × 106 d
5b	10.14	−0.03	1.6 × 107 e
6a	8.18	0.31	1.1 × 106 d
6b	9.00	0.17	8.6 × 106 e

^aDetermined at 298 K in 10 mM potassium phosphate containing 200 mM KCl by plotting the fraction of aryloxide present as a function of pH as in Fig. 1 and fitting to the sigmoidal function f _aryloxide = 10^pH−pK_a/(1 + 10^pH−pK_a).

^bDetermined at 298 K versus Ag/AgCl in 10 mM potassium phosphate containing 200 mM KCl at a scan rate of 10 mV/s.

^cDetermined at 303 K in chlorobenzene and initiated by AMVN as in ref. 37.

^dValues of 3.7 × 10⁶ (5a) and 1.4 × 10⁶ (6a) were determined by the peroxyl radical clock approach.^18c

^eCarried out at 323 K. Values of 11.6 × 10⁶ (5b) and 6.5 × 10⁶ (6b) were determined at 310 K by the peroxyl radical clock approach.^18g