Capturing the elusive aromaticity of bicalicene.
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.
National Medicines Institute Laboratory of Theoretical Methods and Computation, 30/34 Chelmska, 00-725 Warsaw, Poland. wojozim@gmail.com
W P
WP
Oziminski
M
M
Palusiak
J
J
Dominikowska
T M
TM
Krygowski
R W A
RW
Havenith
C M
CM
Gibson
P W
PW
Fowler
D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011083:Polycyclic Compounds / Q000737:chemistry*; D011789:Quantum Theory
D006841:Hydrocarbons, Aromatic; D011083:Polycyclic Compounds; C582386:bicalicene