Redox Potentials for Hydrogen Species in Acetonitrile and Tetrahydrofuran

The properties of the fundamental hydrogen species, proton (H + ), hydrogen atom (H • ), and hydride anion (H – ) are critical to a vast range of chemical processes, yet their thermodynamic properties in nonaqueous solvents are not well established. A hybrid supermolecule-continuum approach is used to predict the Gibbs free energies of solvation (Δ G ° solv ) and standard redox potentials ( E °) for the 2H + /H 2 and H • /H – couples in acetonitrile (MeCN) and tetrahydrofuran (THF) following the approach previously used for water. Gas phase and solution phase structures were optimized with ωB97X-D/aug-cc-pVTZ. Solvation was treated with the SMD self-consistent reaction field model, and CCSD(T)/aug-cc-pVTZ gas phase calculations were used as a benchmark for method sensitivity. For H +, the Δ G ° solv values are predicted to be −258.7 kcal/mol in MeCN and −259.2 kcal/mol in THF. The standard redox potentials for the 2H + /H 2 couple are +0.21 V (±0.1 V) in MeCN and +0.18 V (±0.15 V) in THF relative to the aqueous SHE ( E ° SHE = 4.28 V on the absolute scale), consistent with the available experimental data. The Δ G ° solv for H – is predicted to be −76.9 kcal/mol in MeCN and −67.8 kcal/mol in THF, and for H •, Δ G ° solv is predicted to be 2.1 kcal/mol in both MeCN and THF. These solvation energies yield calculated redox potentials for the H • /H – couple of −0.12 V (±0.3 V) in MeCN and −0.52 V (±0.1 V) in THF relative to the aqueous SHE. H 2 solvation is near thermoneutral in both solvents. The p K a (H 2 ) is predicted to be 43.0 in MeCN and 49.3 in THF. The proton-coupled electron transfer (PCET) accounting term C G was evaluated on the ferrocene scale and deviates from the reported literature values by 7.5 kcal/mol in MeCN and 5 kcal/mol in THF. These results establish an internally consistent thermodynamic framework for hydrogen redox chemistry in MeCN and THF and improve consistency across E °, Δ G ° solv, p K a, and C G .