Table 6.

PCET Thermochemistry of Phenols^a

compound	solvent	E^∘(RO^•/−)	E^∘(ROH^•+/0)	pK_a(ROH^•+)	pK_a(ROH)	E^∘(V vs H₂)^j	BDFE
PhOH	gas	–	–	–	–	1.353	79.8⁴²
PhOH	H₂O	0.79³⁰²	1.5³⁰³	[−2]	10.0⁴⁴	1.38	84.7
PhOH	C₆H₆	–	–	–	–	1.320	82.5^c
4-Me-PhOH	H₂O	0.68³⁰²	1.4³⁰³	[−2]	10.3⁴⁴	1.29	82.5
4-Me-PhOH	C₆H₆	–	–	–	–	1.229	80.4^c
4-MeO-PhOH	H₂O	0.54³⁰²	1.1³⁰³	[0.7]	10.1⁴⁴	1.14	79.0
4-MeO-PhOH	C₆H₆	–	–	–	–	1.082	77.1^c
4-NO₂-PhOH	H₂O	1.22³⁰²	–	–	7.1⁴⁴	1.64	90.6
4-F-PhOH	H₂O	0.76³⁰²	–	–	9.9⁴⁴	1.35	83.8
4-Cl-PhOH	H₂O	0.80³⁰²	–	–	9.4⁴⁴	1.36	84.1
4-Br-PhOH	H₂O	0.82³⁰²	–	–	9.4⁴⁴	1.38	84.5
4-I-PhOH	H₂O	0.82³⁰²	–	–	9.3⁴⁴	1.37	84.4
4-CO₂⁻-PhOH	H₂O	0.90³⁰²	–	–	9.4⁴⁴	1.46	86.4
4-Me(O)C-PhOH	H₂O	1.00³⁰²	–	–	%	1.47	86.8
4-CN-PhOH	H₂O	1.12³⁰²	–	–	7.9⁴⁴	1.59	89.4
4-NH₂-PhOH	H₂O	0.217³⁰²	–	–	10.4⁴⁴	0.833	72.0
4-NH₂-PhOH	DMSO	−1.060^20,i			20.75²⁰	0.839	71.9
4-NMe₂-PhOH	H₂O	0.174³⁰⁴	–	–	10.1⁴⁴	0.772	70.6
1-naphthol	H₂O	0.59³⁰⁵	–	–	9.3³⁰⁵	1.14	79.1
2-naphthol	H₂O	0.69³⁰⁵	–	–	9.6³⁰⁵	1.26	81.8
tyrosine	H₂O	0.71³⁰²	–	–	10.1⁴⁴	1.31	83.0
trolox C^e	H₂O	0.192³⁰⁴	–	–	12.1³⁰⁶	0.908	73.7
HPMC^f	C₆H₆	–	–	–	–	0.884	72.5^c
TocOH^g	C₆H₆	–	–	–	–	0.883	72.5^c
2,4,6-^tBu₃PhOH	H₂O	–	–	–	–	0.983	75.5^d
2,4,6-^tBu₃PhOH	MeCN	[−0.67]	–	–	28^20,h	0.99¹⁹	74.8
2,4,6-^tBu₃PhOH	DMSO	−0.674^20,i			17.8²⁰	1.050	76.8
2,4,6-^tBu₃PhOH	C₆H₆	–	–	–	–	1.014	75.5^b
2,4,6-^tBu₃PhOH	CCl₄	–	–	–	–	1.014	75.3^b
2,4,6-^tBu₃PhOH	THF	–	–	–	–	0.97¹⁹	74.4
2,6-^tBu₂PhOH	C₆H₆	–	–	–	–	1.082	77.0^c
4-Me-2,6-^tBu₂PhOH	C₆H₆	–	–	–	–	1.004	75.3^c
4-MeO-2,6-^tBu₂PhOH	C₆H₆	–	–	–	–	0.887	72.6^c
4-MeO-2,6-^tBu₂PhOH	MeCN	–	–	–	–	0.868¹⁹	72.0
4-MeO-2,6-^tBu₂PhOH	THF	–	–	–	–	0.838¹⁹	71.3

Potentials 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 $\frac{1}{2} H_{2 (g)}$ addition. Uncited values of E^∘(V vs H₂) were calculated from other values in the row using Scheme 2 or eq 16. BDFEs 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. Values in [square brackets] have been calculated from the other values in the row using Hess’ law.

Calculated from previously estimated BDEs in ref 33 but using hydrogen enthalpy of solvation (ΔH^∘solv[H₂]_s) values reported for C₆H₆ and CCl₄ in ref 48.

Calculated relative to 2,4,6-^tBu₃PhOH by applying the difference in BDFEs reported in ref 29.

Calculated from the PCET potential reported in ref 307 and extrapolating to pH 0.

Trolox C = (±)-6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid.

HPMC = 6-hydroxy-2,2,5,7,8-pentamethylchroman.

TocOH = α-tocopherol.

Extrapolated from DMSO to MeCN using the method of Kütt and co-workers.²⁹⁸

ⁱ

Calculated from the reported anodic peak potentials, assuming a 57 mV peak-to-peak separation.

Compared with other solvents, both E^∘(V vs H₂) and BDFE values in DMSO have larger uncertainties from the thermochemical constants E^∘(H⁺/H₂) and CG (see Table 1).