Capturing the elusive aromaticity of bicalicene

Phys Chem Chem Phys. 2013 Mar 7;15(9):3286-93. doi: 10.1039/c2cp43426a. Epub 2013 Jan 29.

Abstract

The ring-current aromaticity of the bicalicene molecule arises, in spite of the 16 π carbon perimeter, from strong local diatropic circulations on the two pentagonal rings, as shown by current-density maps computed at the ipsocentric RHF/6-311G** and DFT/6-311G** levels of theory. Conjugated-circuit models cannot capture this pattern of circulation as it arises from 'ionic' contributions in a valence-bond picture. Canonical molecular-orbital analysis reveals a cancellation of paratropic and diatropic frontier-orbital contributions, which explains the difficulties that Hückel-based models have in producing qualitatively correct current-density maps for this molecule. Other measures of aromaticity reflect, to different extents, the dominance of the 'tetraionic' contribution to the aromaticity of this species.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Hydrocarbons, Aromatic / chemistry*
  • Models, Molecular
  • Molecular Conformation
  • Polycyclic Compounds / chemistry*
  • Quantum Theory*

Substances

  • Hydrocarbons, Aromatic
  • Polycyclic Compounds
  • bicalicene