Electron density based characterization of π bonds in planar molecules.

A new method has been developed to detect and analyze molecular π systems. The concept of bonding critical point is generalized to electronic π systems, and it is shown how a π bond can be characterized via the corresponding bond critical point (BCP) in planar molecules. In this context, charge density and its Laplacian at the BCP(π) of a strongly delocalized π system can be distinguished from that of a localized one. The presented formalism is applied to three types of nanoconductors as conjugated polyenes, which revealed the alternative pattern of the double bonds. Also, several cyclic conjugated molecules are considered to explore their π electronic structure and aromaticity.