Brønsted acidity of H-adatoms at protic solvent-transition metal interfaces and its kinetic consequences in electrophilic addition reactions

H-adatom (H*) at protic solvent-metal interfaces can undergo ionization and form interfacial protons (H-Metal_solvated → H⁺_solvated + Metal^-_solvated, K_a,HM). A three-dimensional Born-Haber thermochemical framework quantitatively decomposes the H* acidity (as K_a,HM) into the metal's work function, H-binding energy, H⁺/H• reduction potential, and thermodynamic properties of gaseous H₂ or H•, capturing the separate contributions from metal, adsorbate, and solvent. On Group VIII metals, the K_a,HM increases from left to right and top to bottom of periodic position and spans 20 orders in magnitude. The interfacial protons, together with transition metal surfaces, are much more effective than free protons for the electrophilic addition of deuteron that leads to the selective C_ar-H/C_ar-D exchange on the ortho and para carbon atoms of phenol because of the additional stabilization afforded by the transition metals acting as a Brønsted base. Hydrogen is required, but the reactive protons inherit the chemical fingerprint from the protic solvent.