Quantifying Superacidity with Density-Based Reactivity Theory

Superacids, defined as compounds exhibiting acidities stronger than sulfuric acid, are essential in catalysis, synthesis, and material chemistry. Yet the quantitative understanding of their intrinsic acidity remains challenging due to the complex interplay of charge delocalization, resonance, and solvation effects. In this work, we employ density-based reactivity theory to describe and predict the equilibrium acidities of two major families of superacids—nitrogen-centered and carbon-centered species—each comprising multiple molecular series with experimentally measured pKₐ values available in 1,2-dichloroethane. Descriptors derived from conceptual density functional theory, information-theoretic approach, and topological analysis at bond critical points were systematically evaluated. Strong linear correlations between calculated descriptors and experimental pKₐ values were observed for N-centered superacids, confirming the robustness of density-based quantities in capturing intrinsic acidity. In contrast, weaker correlations for C-centered analogues reveal the multifaceted origins of their superacidity. Multi-descriptor regression further improves quantitative agreement across all systems. These findings demonstrate that superacidity is an emergent, electron density associated phenomenon that can be rationalized and predicted within the density-based reactivity framework.