Characterization of Local Aromaticity in Polycyclic Conjugated Hydrocarbons Based on Anisotropy of π‐Electron Density

Abstract

In recent contributions, it was demonstrated that the anisotropy of π‐electron density could be considered as a reliable descriptor to probe the aromaticity in a wide range of annulene and hetero‐monocyclic compounds. The electron density anisotropy on a plane can be simply measured by the ratio of two in‐plane Hessian eigenvalues associated with the eigenvectors lying in the plane. This descriptor is undirected and has a circular symmetry for aromatic rings, whereas it is directed and has an elliptical shape in antiaromatic cycles. This research takes a step forward towards the extension of this approach to polycyclic conjugated hydrocarbons. The obtained results show that the anisotropy of the π‐electron density works nicely for the assessment of local aromaticity in polycyclic compounds. This finding provides clear evidence to have a universally successful aromaticity descriptor based on the topological properties of one‐electron density distribution.

Antiaromaticity–Aromaticity Interplay in Fused Benzenoid Systems Using Molecular Electrostatic Potential Topology

“…The dilution in antiaromaticity in such fused systems could be brought in by adopting a stable configuration that avoids double bond localization within the antiaromatic rings. Theoretical studies , on A–aA fused systems were mainly focused on the energetic aspects of the π-conjugation, − ring current features, − and magnetic properties , such as nuclear-independent chemical shift. In these studies, the computed molecular descriptors were related to the local aromaticity, that is, the aromaticity expressed within a ring. − …”