How aromatic are large (4n + 2)pi annulenes?
[structure: see text] While the total aromatic stabilization energies (ASE) of the [n]annulenes, from C(6)H(6) to C(66)H(66), converge to ca. 22 kcal/mol, the ASEs per pi-electron decrease markedly. Bond length alternation (which depends on the theoretical level) only reduces stabilization somewhat but influences the magnetic properties (NICS, proton chemical shifts, and magnetic susceptibilities) considerably. Nevertheless, these magnetic criteria, when based on the most realistic structures, agree that the aromaticities of the larger annulenes decrease and then nearly vanish.
Wannere
Chaitanya S
CS
Computational Chemistry Annex, Department of Chemistry, University of Georgia, Athens, Georgia 30602-2525, USA.
von Ragué Schleyer
Paul
P