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. Author manuscript; available in PMC: 2022 Jun 8.
Published in final edited form as: Chem Rev. 2021 Dec 20;122(1):1–49. doi: 10.1021/acs.chemrev.1c00521

Table 16.

Thermochemical Data for Indoles and Tryptophana

compound solvent E∘(R2N•/−) E∘(R2NH•+/0) pKa(R2NH•+) pKa(R2NH) E∘ (V vs H2) BDFE
indole   H2O   [0.52]   1.24342   4.9342    17.0343   1.53   88.1
tryptophan   H2O   [0.43]   1.15344   4.7344    16.8343   1.43   85.7
2-CH3-indole   H2O   --   1.10342   5.7342    --   1.44   85.9
3-CH3-indole   H2O   [0.38]   1.07342   5.0342    16.6343   1.37   84.3
2,3-CH3-indole   H2O   --   0.93342   6.1342    --   1.29   82.6
a

Potentials for 1e− reductions are in V vs SHE. Values for E∘(V vs H2) are in V; – eE∘ is the average free energy for 12H2(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.