Structures Prediction and Aromaticity for Polycyclic Hydrocarbons

Abstract

The combination method between asymmetric Kekule structures (CMAK) was expanded to the structure prediction of acenes and phenylenes seriese. The predicted structures by the CMAK correspond to those calculated ab initio CASSSCF and CCSD(T) MO and B3LYP density functional methods. The CMAK can characterize the structures. The aromaticity for whole ring and each ring in the treated compounds was estimated by the index of deviation from aromaticity (IDA), was proposed by us in the previous. The estimated aromaticity corresponds fairly to the characterization of the structure predicted by the CMAK. The predicted structures of linear acenes indicate the aromaticity of the central ring and also explain the reactivity for the central ring from the characterized aromaticity. For [n]phenacenes, the side ring in the compompounds indicates much aromaticity. From the position of the much aromaticity for linear acenes and [n]phenacenes, the difference of the reactivity for these compounds can be explained. For the isomers of benzo[1,2:4,5]dicyclobutene and benzo[1.2:5,6]dicyclobutene, the critical difference of the structure and the aromaticity for the central six-membered-ring was explained.