The homotropenylium cation: a system with a pinched π ring current

Mark Lillington, Remco W. A. Havenith, Patrick W. Fowler, Jon Baker, Leonardus W. Jenneskens
2014 Physical Chemistry, Chemical Physics - PCCP  
The homotropenylium cation (1, C 8 H 9 + ) is a key species in the discussion of homoaromaticity. Constrained optimisations around the minimum structure have been performed, varying the size of the gap spanned by the CH 2 -bridge and optimising all other geometrical parameters. At each bridging distance, ab initio currentdensity maps have been calculated and plotted using the ipsocentric approach. Analysis of the maps, including decomposition into localised orbital contributions, gives a clear
more » ... ons, gives a clear indication of a global diatropic ring current passing through the gap. The change in p p -p p interaction, from conventional p overlap around the conjugated seven-carbon perimeter to s overlap (p s -p s ) in the gap, results in a distinctive pinched topology, with two streams of current pinched down into one for part of the circuit. This ring current is diatropic and therefore the species 1 is aromatic on the magnetic criterion.
doi:10.1039/c4cp01075b pmid:24803165 fatcat:fkpa463ourdvhof27s3okff4ka