where R is the gas constant, T is 298.15 K, and the Gibbs free energies (∆G) of the carboxylate anion and the carboxylic acid were calculated using DFT at the M06-2X/6-31+G(d)/SMD(sSAS,H2O)//B3LYP-D3(BJ)/6-31+G(d) level of theory under standard conditions (i.e., 298.15 K, 1 mol/L). A modified scaled solvent-accessible surface (sSAS) approach was used in the SMD solvation model. The value 270.29 kcal/mol was used for the Gibbs free energy of a proton in aqueous solution (∆𝐺 , & ). This is calculated from the sum of the gasphase free energy of proton (-6.28 kcal/mol) and its hydration free energy 44 (-265.9 kcal/mol). Similar to Hammett constant for substituted aryl groups, a negative σHet value indicates a more electron-donating heteroaryl compared to phenyl, whereas a positive σHet indicates a more electron-withdrawing heteroaryl. While traditional aryl Hammett substituent constants often fall in a range of approximately -1 to +1, σHet values exhibit a broader range (Fig. and), showcasing the electronic diversity of heteroaryl groups. Regioisomers of the same parent heteroarene could offer significant variance in their σHet values (e.g., 0.91, 0.71, and 1.33 for 2-pyridyl, 3-pyridyl, and 4-pyridyl, respectively, Fig. ). Further, while 5-membered rings such as pyrrole are known to be often more electron-donating than 6-membered rings such as pyridine, these rings can be tuned using electron-withdrawing groups to alter their electronic properties (Fig. ). 2. Other Electronic Descriptors. Electronic properties such as HOMO and LUMO energies, total dipole moments, and quadrupole moments were extracted from Gaussian 16 single-point energy output files using the Python-based cclib library. From these values, the chemical potential, HOMO-LUMO gap, global electrophilicity, and global nucleophilicity were derived. The chemical potential was calculated from the average of the HOMO and LUMO energies , while the HOMO-LUMO gap is the energy difference between these orbitals. Global electrophilicity (electrophilicity index) was determined using the formula 𝜔 = -$ ./ where μ is the chemical potential and η is the HOMO-LUMO gap. Global nucleophilicity (nucleophilicity index) was computed as the inverse of global electrophilicity (𝑁 = 1 𝜔 ). The HOMO and LUMO coefficients of the ipso carbon were extracted directly from the Gaussian 16 outputs (keyword: pop=(orbitals=10,ThreshOrbitals=5)). Partial atomic charges were computed using Natural Population Analysis (NPA), Hirshfeld, and Charge Model 5 (CM5) charge schemes for the ipso carbon and the sum of the atomic charges of the heteroaryl group in the ArHet-H, ArHet-CO2H, and ArHet-CO2 -compounds.