Computational estimation of the acidities of some inorganic nitrogen acids

ABSTRACT

The pK_a 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 pK_as 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 pK_as 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 pK_as. 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.

KEYWORDS:

• pKa
• QSAR
• inorganic nitrogen acids
• acidities
• density functional theory

Disclosure statement

No potential conflict of interest was reported by the author.