Table 9.

PCET Thermochemistry of Ascorbates^a

compound	solvent	E∘(Asc•−/2−)	E∘(AscH•/−)	pKa(Asc•)	pKa(AscH−)	E∘(V vs H2)	BDFE
AscH−b	water	0.015321	0.72322	−0.45322,323	11.3321,322	0.684	68.6
iAscH−c	MeCN	[−1.07]	--	--	28.8324	0.663	67.3324,d
compound	solvent	E∘(AscH2•+/0)	E∘(AscH•/−)	pKa(AscH2)	pKa(AscH2•+)	E∘ vs H2	BDFE
AscH2e	water	--	0.72322	4.0321,322	--	0.96	74.9
iAscH2f	MeCN	--	−0.41324	18.3324	--	0.70	68.2
compound	solvent	E∘(Asc0/•−)	NA	pKa(Asc•)	NA	E∘(V vs H2)	BDFE
Asc•−	water	−0.14321	--	−0.45322,323	--	−0.17	49.0

^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. Uncited values of E^∘(V vs H₂) were calculated from other values in the row using Scheme 2 or eq 18. BDFEs are in kcal mol⁻¹ and if uncited were calculated from E^∘(V vs H₂) using eq 18. Values in [square brackets] have been calculated from the other values in the row using Hess’ law.

^bAscH⁻ = ascorbate.

^ciAcsH⁻ = 5,6-isopropylidene ascorbate.

^dA quasi-reversible potential is reported in ref 324, but we prefer the use of the BDFE from equilibration with TEMPO.

^eAscH₂ = ascorbic acid.

^fiAscH₂ = 5,6-isopropylidene ascorbic acid.