Quantum chemical topology based on the Kohn-Sham one-electron potential for investigating the reaction mechanisms of nitrogen-centered radicals.

Herein, we report the application of quantum chemical topology derived from the Kohn-Sham one-electron potential (KSpot) to open-shell nitrogen-centered radicals. Using 50 representative radicals, the effectiveness of KSpot atomic charges in characterizing the electronic structures of open-shell radical systems was evaluated. KSpot charges show strong linear correlations with QTAIM and Hirshfeld charges and reproduce the electrostatic potential reasonably well; stratified analyses over 50 radical systems by chemical environment and element type further support its applicability. Analysis along the intrinsic reaction coordinate of radical addition reactions reveals a synergistic evolution between KSpot charges at the reactive center and system energy. Combining the KSpot molecular face with spin-density analysis, the evolution of total electron density and unpaired electrons along the reaction pathway was characterized. Quantitative analysis reveals a linear correlation (R = 0.9740) between the KSpot charges at the reactive site of the reactants and the reaction activation energy, though this correlation is based on a limited set of substrates and requires further validation. This study extends the KSpot method to open-shell systems and preliminarily explores a potential quantitative relationship between reactant charge distribution and reaction barrier, suggesting that KSpot charges may serve as a physicochemical descriptor for nitrogen-centered radical reactions, though further validation with a larger dataset is required.