Aromaticity with a twist:: Mobius [4n]annulenes

[GRAPHICS] Aromatic Mobius [4n]annulenes with 4n pi electrons, originally conceived by Heilbronner, are characterized computationally. These (CH)(12), (CH)(16), and (CH)(20) minima have nearly equal C-C bond lengths, small twist angles around the rings, and magnetic properties (NICS, nucleus-independent chemical shifts-see above at various positions in [16]annulene-and magnetic susceptibility exaltations) indicating significantly diatropic ring currents. The Mobius forms are not the most stable isomers but may contribute significantly to the chemistry of these annulenes.