Table 11.

PCET Thermochemistry of Dioxygen Reduction^a

HO2•/HOOH	solvent	E∘(HOOH•+/0)	E∘(HOO•/−)	pKa(HOOH•+)	pKa(HOOH)	E∘(V vs H2)	BDFE
HOOH	gas	–	–	–	–	1.24242	77.2
HOOH	H2O	–	[0.77]	–	11.672	1.4645	86.5
O2(g)/•OOH	solvent	E∘(HOO+/•)	E∘(O20/•−)	pKa(HO2+)	pKa(HO2•)	E∘(V vs H2)	BDFE
•OOH	gas	–	–	–	–	−0.15042	45.1
•OOH	H2O	–	−0.3545	–	4.845	−0.0745	51.2
O2•−/−OO–H	solvent	E∘(HOO•/−)	E(O2•−/2−)	pKa(HO2•)	pKa(HOO−)	E∘(V vs H2)	BDFE
−OO–H	H2O	0.77b	–	4.845	–	1.05	77.1
O2(g) + 2H2(g) → 2H2O	solvent					E∘(V vs H2)	−ΔG∘/nc
O2/H2O	gas					1.18542	75.9
O2/H2O	MeCN					1.2467	80.6
O2/H2O	DMF					1.2667	81.4
O2/H2O	DMA					1.23751
O2/H2O	H2O					1.229327	81.1
O2(g) + H2(g) → H2O2	solvent					E∘(V vs H2)	−ΔG∘/nc
O2/H2O2	gas					0.54642	61.2
O2/H2O2	H2O					0.695327	68.8
H2O2 + H2(g) → 2H2O	solvent					E∘(V vs H2)	−ΔG∘/nc
H2O2/H2O	gas					1.82342	90.6
H2O2/H2O	H2O					1.76345	93.5

^aPotentials for 1e⁻ reductions are in V vs SHE if in aqueous solution and V vs Cp₂Fe^+/0 if they are in organic solution. Values for E^∘(V vs H₂) are in V; – eE^∘ is the average free energy for $\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.{\text{H}}_{2(\text{g})}$ addition. BDFEs and −ΔG^∘/n are in kcal mol⁻¹ and if uncited were calculated from E^∘(V vs H₂) using eq 18. In many cases the citation associated with a BDFE is for the related BDE, and the tabulated value was calculated using eq 9.

^bE^∘(HOO^•/−) has been calculated using the H₂O₂ pK_a and HO₂^•/HOOH PCET potential in water.

^c−ΔG^∘/n values are average free energies for the overall reaction shown except to form H^• [rather than add H_2(g)]. See Section 4.