The maxima of MESP show a strong correlation with pKa values for anilines and phenols their additivity rule . They observed a strong linear correlation of the experimental pKa values of singly substituted benzoic acids with the MESP at the leaving proton and the MESP on the acidic oxygen atom (depicted in Figure ). A 2012 study investigating the proton affinity and gas-phase basicity of 14 heterocyclic aromatic compounds, each containing at least two nitrogen atoms, uncovered a strong correlation between variations in their total energy and corresponding MESP values. This correlation was particularly evident when comparing the lowest and second lowest MESP associated with the nitrogen atoms . Wang and Cheng used MESP on the proton-donating atom of a series of neutral aromatic hydroxyl-substituted photoacids to study the relationship between excited-state acidities pKa* and MESP on the protondonating atom. They revealed that a basic MESP on the proton-donating nucleus serves as a valuable theoretical descriptor, providing sufficient accuracy to capture system-dependent pKa variations . Liu and Pedersen created an effective approach for estimating molecular pKa values using either the MESP on the nucleus of the acidic atom or the sum of valence natural atomic orbitals (NAO) . They observed a unique linear relationship between the difference in MESP (the MESP is subtracted by the isolated atomic MESP for each category of compounds) and experimental pKa data of amines, anilines, carbonyl acids, alcohols, sulfonic acids, thiols, and their substituents.