Reactivity Indices and Theoretical Estimation of Acidity Constants of Diphenylphosphine Oxides in Dichloromethane

This study to evaluate the tautomeric stability of diphenylphosphine oxides using density functional theory (DFT/B3LYP/6-31+G*) calculation in dichloromethane solution. The results reveal that stability of the tautomers is closely dependent on the electronic nature of the substituents. Specifically, the trivalent pentavalent form (PV) is favored when the substituents exert an electron-donating effect. Conversely, the trivalent form (PIII) becomes more stable in the presence of electron-withdrawing groupe. PIII tautomer, characterized by its nucleophilic nature, exhibits enhanced nucleophilicity when the phosphorus moiety is present as the deprotonated phosphinite anion. The deprotonation reaction leading to this ionic form allowed the estimation of pKa values for diphenylphosphine oxides. These pKa values also show a significant dependence on substituent nature, highlighting the influence of electronic effects on the acidity of these compounds.