Quantum-Chemical Predictions of Absolute Standard Redox Potentials of Diverse Organic Molecules and Free Radicals in Acetonitrile

Abstract

A calibrated B3LYP/6-311++G(2df,2p)//B3LYP/6-31+G(d) method was found to be able to predict the gas-phase adiabatic ionization potentials of 160 structurally unrelated organic molecules with a precision of 0.14 eV. A PCM solvation model was benchmarked that could predict the pK(a)'s of 15 organic acids in acetonitrile with a precision of 1.0 pK(a) unit. Combining the above two methods, we developed a generally applicable protocol that could successfully predict the standard redox potentials of 270 structurally unrelated organic molecules in acetonitrile. The standard deviation of the predictions was 0.17 V. The study demonstrated that computational electrochemistry could become a powerful tool for the organic chemical community. It also confirmed that the continuum solvation theory could correctly predict the solvation energies of organic radicals. Finally, with the help of the newly developed protocol we were able to establish a scale of standard redox potentials for diverse types of organic free radicals for the first time. Knowledge about these redox potentials should be of great value for understanding the numerous electron-transfer reactions in organic and bioorganic chemistry.

Computational Redox Potential Predictions: Applications to Inorganic and Organic Aqueous Complexes, and Complexes Adsorbed to Mineral Surfaces

“…Using the direct method for the redox potentials prediction, another computational study calculated the redox potentials of 250 distinct organic compounds in DMSO solution [108] by employing the B3LYP DFT functional and including solvation effects using the integral equation formalism polarizable continuum model (IEFPCM) solvation. Interestingly, in this study, the calculated ionization potential at the gas-phase by the B3LYP method were corrected by 0.28 eV, as obtained from an earlier study [107]. Using this correction, the direct method applied for predicting redox potentials of different organic compounds in DMSO solution were within a MUE of 0.11 eV with respect to the experimental redox potentials [108].…”

“…By employing the B3LYP/PCM method, redox potentials of 270 different organic compounds in acetonitrile solvent were calculated [107]. Of these 270 compounds, this study calculated adiabatic ionization potentials of 160 organic compounds, for which the experimental ionization potentials were accurately known.…”

“…Of these 270 compounds, this study calculated adiabatic ionization potentials of 160 organic compounds, for which the experimental ionization potentials were accurately known. The calculated IPs were plotted with respect to experimental IPs, and the plot produced an intercept value of 0.28 eV, which corresponds to underestimation of IPs [107]. This was added as a correction to predict the redox potentials of the complete investigated set with respect to the SHE reference potential.…”

Theoretical calculations of the relative pKa values of some selected aromatic arsonic acids in water using density functional theory

“…The pKa is the most important characteristic for comparing the acidity of a series of compounds. [16][17][18][19] The pKa value also indicates the ratio of neutral and anionic forms of a molecule at a given pH. 20 The large number of papers describing computational research on the prediction of the acidity of various compounds in the recently published chemical literature indicates that the pKa is one of the important properties in many scientific domains such as chemistry and biology.…”

“…22 The experimental determination of pKa values in reaction intermediates, specific parts of large biological building blocks, and molecules with dissolution limitations is very difficult to obtain. 18,19,23 In addition, providing standard conditions for the experimental determination of pKa value is essential for allowing comparison of different results. Accordingly, many researchers are tending to calculation of pKa values using theoretical and computational approaches.…”