A case of breakdown of the Kekulé-structure model

Abstract

For a long time, Kekulé structures have been used to predict and rationalize the stability, geometry, and π-electron properties of polycyclic conjugated molecules, especially hydrocarbons. We now point out an example, demonstrating that the Kekulé-structure model is not generally applicable. Namely, the molecule of dibenzo[cd,mn]indeno[123, gf ]pyrene is perfectly planar and strain-free. Yet, its geometry (determined by means of an unrestricted symmetry-broken UB3LYP/6-311G(d,p) DFT method) is in complete disagreement with what one would expect on the basis of its Kekulé structures. © Taylor & Francis Group, LLC.