Comment on "The electron-pair origin of anti-aromaticity: Spectroscopic manifestations"

In the article by Zilberg and Haas, “The Electron‐Pair Origin of Anti‐aromaticity: Spectroscopic Manifestations,” the relative sign of the two Kekulé valence bond functions, R and L, in conjugated cyclic hydrocarbons was discussed. It was proposed that in the ground‐state wave function of aromatic compounds, the two functions contribute with like sign, while in the ground state of anti‐aromatic compounds, the two functions contribute with opposite sign. In this Comment, it is shown that the two functions enter with like sign also into the ground‐state wave function of anti‐aromatic compounds. Furthermore, it was argued that resonance tends to (de)stabilize a symmetric ground‐state geometry in case of the (anti‐)aromatic compounds. The expression derived by Zilberg and Haas for the stabilization energy shows an unusual dependence on the ring size and distortion coordinate. An alternative formula is derived for the stabilization energy, in which the energy depends quadratically on the distortion coordinate. Without further numerical calculations, it is not possible to predict whether this term will (de)stabilize a symmetric geometry of the ground state of (anti‐)aromatic molecules. Rather, we are led to believe that the influence of term in question on the geometric stability may be small, thus not providing the main reason for the geometric distortion of anti‐aromatic compounds. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007