Computational estimation of the acidities of some inorganic nitrogen acids

Abstract

ABSTRACTThe pKa of a compound is among the compound's most useful properties since it defines the forms of the compound present under different conditions. In a previous report [Seybold, Mol. Phys. 113, 232 (2015)], computational estimates of the pKas of inorganic oxygen acids were presented using linear free energy methods based on quantum chemical descriptors. Like the oxygen acids, inorganic nitrogen acids encompass a diverse set of chemically and commercially important compounds, and this work explores computational modelling of the pKas of inorganic nitrogen acids and related compounds. Computations were performed at the DFT B3LYP/6-31+G** level with the SM8 aqueous solvent model of Marenich et al. [J. Chem. Theory Comput. 3, 2011 (2007)]. The energy difference ∆E(H2O) between the nitrogen cation acid and its neutral conjugate base, as determined within the SM8 aqueous solvent, provided good correlations (R2 = 0.921) with the experimental pKas. As shown also in other studies, it appears that the descriptor ∆E(H2O) can act as a useful proxy for the Gibbs energy change ∆G˚(H2O) of the acid dissociation process HA+ A + H+ for the majority of the inorganic nitrogen acids examined in this study.