where qA is the Hirshfeld charge on A. This result shows that under the first-order approximation, the information gain due to the formation of a molecular system gives rise to the Hirshfeld charge, and the information before and after the system is formed should be conserved. The reason why information gain and Hirshfeld charge can be employed to quantify electrophilicity and nucleophilicity is because, when a new system is formed, the identity of its components will be preserved. If a component is electrophilic in nature before the new system is formed, it will still be so afterwards. Moreover, to preserve the identity as much as possible, the new system adjusts its components in such a way that each component becomes charged according to the stockholder partition scheme. Therefore, the amount of the information gain and Hirshfeld charge becomes the identity indicator of each component in the new system. In Fig. , we examined 21 electrophilic systems with known electrophilicity scale and, in Fig. , compared our theoretical results with experimental values. In Fig. , we considered 22 nucleophilic molecules with known experimental nucleophilicity scale and, in Fig. , compared our information gain and Hirshfeld charge results with the experimental values. Strong linear correlations in both cases between theoretical and experimental results are seen, suggesting that information gain and Hirshfeld charge can simultaneously be applied as robust descriptors of electrophilicity and nucleophilicity. We recently compared the performance of these two approaches. Regioselectivity and stereoselectivity. Regioselectivity is the susceptibility of a bond making and breaking process to preferentially take place at one site/atom of a molecule over all other possible places. A prominent example is the group directing effect for electrophilic aromatic substitution reactions, where the position, ortho/para or meta, of the substitution depends on the nature of the group -R already attached on the benzene ring. For groups like R = -Me, -NH2 and -OH, the preferred substitution site is at the ortho/para position, but for groups such as R = -NO2, -CN, and -SO3H, the meta position is favored. Using information gain or Hirshfeld charge, such regioselectivity propensity can be satisfactorily rationalized. We also examined regioselectivity with these ITA quantities for other systems and compared the performance with Fukui functions from the CDFT framework. For stereoselectivity, which is the tendency of the preferential formation in a reaction of one stereoisomer over the other, it can be rationalized by the quantification of the steric effect in the OF-DFT framework introduced in Eq. ( ). This is done through the potential associated with the steric energy ES[] defined by the functional derivative with respect to the electron density, 8