Synthesis and properties of the first Mobius annulenes

Heilbronner in 1964 predicted that annulenes with ... a planar perimeter of N=4r AO's, which would yield an open shell configuration when occupied by 4r electrons, can be twisted into a closed shell Mobius strip perimeter without loss in it electron energy. We have been able to synthesize the first [4n]annulene with such a Mobius topology and now present further Mobius isomers and the details of their preparation as stable compounds. To address the question whether the twist in the a system has an effect on the properties we systematically investigate energy, geometry and magnetic parameters of a large number isomers of [16]annulenes. The Mobius twisted annulenes are consistently more aromatic than the non-twisted isomers. This is true for the parent as well as our benzoannelated systems. Our results are in contrast to those published recently by C. Castro, W L. Karney, P. von R. Schleyer et al.