Application of Electron Delocalization Indicators in the Study of Electrophilic Aromatic Substitution Reactions

Abstract

Electron delocalization is a fundamental concept in chemistry. It is deeply rooted in many important chemical phenomena e.g. aromaticity, conjugation and the reactivity of a vast number of inorganic, organometallic and organic compounds. This review focuses on those theoretical studies in which electron delocalization indicators provide valuable insigths in the understanding of electrophilic aromatic substitutions. The considered approaches to deal with electron delocalization include primarily the quantum theory of atoms in molecules but also briefly the analysis of the electron localization function, the topography of the molecular electrostatic potential, the anisotropy of the induced current density and GIAO-derived charge delocalization modes. We go over the characterization of the electron delocalization in the most important intermediates of the electrophilic aromatic substitutions namely the Wheland intermediates and the complexes formed by aromatic molecules and electrophiles. Then we discuss the relation between aromaticity and electrophilic aromatic substitutions. Finally, we give an account of the importance of the electron delocalization in the effect of the substituents on the regiochemistry and reactivity of an aromatic molecule towards an electrophilic attack. Besides reviewing the literature in an extensive way, it is our hope that this review will suggest directions of further progress in the field.

Properties of atoms in electronically excited molecules within the formalism of TDDFT

“…Usually, the analysis of excited states is done in terms of geometry modifications, molecular orbitals, dipole moments, and the electron density difference between the ground and the excited state of interest . Recently, the analysis of the topological properties of the electron density ( ) at different levels of theory such as CIS, CASSCF, CASPT2, and EOM‐CCSD has given insights about the electronic structure and properties of molecules in an excited state, in a similar fashion that for the ground state (GS) . Density functional theory (DFT) instead of its time‐dependent counterpart, TDDFT, has also been used to obtain electron densities for low‐lying singlet and triplet excited states of organometallic compounds .…”