A Conceptual Density Functional Theory-Based Maximum Nucleophilicity Principle

We introduce a variational formulation of nucleophilicity within the framework of conceptual density functional theory (CDFT), thus proposing a maximum nucleophilicity principle (MNP), in formal analogy to the established minimum electrophilicity principle (MEP). Starting from a third-order Taylor expansion of the electronic energy with respect to the number of electrons at constant external potential, we extend our recently proposed global nucleophilicity index NG derived from the chemical potential μ, hardness η, and hyperhardness γ. We demonstrate that this index follows a well-defined variational condition for electron-loss processes. An explicit functional differential expression is derived for NG[N, v(r)], enabling a thermodynamically consistent description of nucleophilic behavior. The principle is evaluated across a set of six benchmark reactions. The results confirm the concurrent validity of MNP and MEP as complementary conceptual tools for understanding electron transfer in chemical reactivity.