The nature of intramolecular interactions determining the σ− constants for aromatic systems

Density functional theory computations at the B3LYP/6-311+G(2d,2p) level for a series of 25 para-subsituted phenoxide ions were performed in analyzing the intramolecular effects determining the σ− reactivity constants for aromatic systems. Very good linear relationships were established between the electrostatic potential at nuclei values, NBO and Hirshfeld atomic charges at the phenoxide oxygen in p-substituted phenolates and the σ− constants. Comparisons of the charge shifts induced by polar groups at para position in the phenoxides and in substituted at position 4 bicyclo[2.2.2]octan-1-olates reveals that very strong conjugative effects determine the high values of σ− constants for electron-withdrawing substituents. Inversely, low charge transfer between substituents and the negatively charged reaction center in the case of electron donating groups is in harmony with the low values for the σ− constants for such moieties. The unusual resonance interactions between substituents and the negatively charged reaction center were quantitatively assessed.