Insight into The Nature of Rim Bonds in Coronene.

Coronene is known in chemistry as an aromatic or even superaromatic molecule while it has 24 π-electrons which does not conform to the 4 n + 2 Huckel's rule. Chemical bonding description of it is not settled in chemistry and five models were reported in the literature. According to our model, coronene has two concentric π-systems responsible for aromaticity inside of the molecule. In addition to that there are six peripheral 2c-2e π-bonds, which makes coronene aliphatic/aromatic at the same time. However, recent experiments and calculations put in question the presence of peripheral π-bonds. In order to resolve this issue, we computationally studied reaction mechanism of the Cl molecule with CH, CH, and CH. As it turned out, coronene behaves in a way similar to ethylene by adding Cl molecule. Thus, it proves that coronene indeed has peripheral double bonds which is also consistent with its experimental geometrical features. Our chemical bonding model allows to identify the most reactive atoms in coronene and other PAHs; therefore, it is a matter of importance for combustion and soot formation studies.