Comparative study of aromaticity in tetraoxa[8]circulenes

Abstract

A detailed analysis of the local aromaticity in tetraoxa[8]circulene and its benzo-annelated derivates was performed by means of the energy effect (ef), multicenter delocalization indices (MCI), harmonic oscillator model of aromaticity (HOMA) index, nucleus independent chemical shifts (NICS), and ring current maps. According to the indices employed, the central ring of tetraoxa[8]circulene is antiaromatic, whereas the benzenoid and furanoid rings are aromatic. The calculated current density distribution in tetraoxa[8]circulenes showed that the annulene within an annulene model of aromaticity is not applicable for these compounds. It was found that the presence of benzo-annelated rings enhances (respectively diminishes) aromaticity (respectively antiaromaticity) of the five-membered (respectively eight-membered) rings in tetraoxa[8]circulenes. These effects are found to be proportional to the number of benzo-annelated rings. The observed regularities can be rationalized by means of the pairwise energy effect (pef) of cyclic conjugation. © 2012 American Chemical Society.