The π-electron delocalization of phenol–fluoride system in explicit solvent conditions

The hybrid quantum chemical (QM/MM) model of the environment was used for characteristics of π-electron delocalization in aromatic ring of phenol–fluoride complex. The inductive effect of approaching fluoride on aromaticity of phenol was quantified by 27 aromaticity indices in the presence of explicit first hydration layer. Observed changes in aromaticity of the phenol aromatic ring cannot be described by a single aromaticity index and a vector of eight contributions was proved to be indispensible. The selection of these the most representative aromaticity measures was performed by means of Principal Component Analysis (PCA). It was demonstrated that significant and subtle role of explicit water molecules on extend of π-electron delocalization. The values of indices such as hardness (η), ATI, NICS(1) and DRE are sensitive to approaching fluoride and increase their values in polar conditions. On the other hand, such indices as BAC, Lagrangian form of kinetic energy density estimated at ring critical points and Shanon-like entropy are mostly dependent on the conformation of the first solvation layer and are less susceptible to the separation distance of fluoride. Thus, multidimensional nature of aromaticity is even more complex if direct intermolecular interactions are taken into account in water solutions.