Published by admin on 09 May 2008
Aromatics with a twist
In the 1930s, the physical chemist Erich Huckel predicted that annulenes containing 4n+2 mobile electrons should be stable (aromatic), and that those with 4n electrons should be unstable (antiaromatic) [1]. His prediction spurred a number of synthetic chemists to prepare these molecules. Each successful synthesis confirmed Huckel’s predictions. But in 1964, a spectacular theoretical prediction was made: the Huckel rules are reversed for annulenes with a 180° twist (so-called Mobius annulenes [2]). High-level theoretical calculations confirmed that Mobius rings with 4n electrons are indeed truly aromatic, whereas those with 4n+2 electrons are antiaromatic. Synthetic chemists once again rushed to prove the prediction experimentally, but all early attempts failed. It wasn’t until 2003 that the first synthesis of a Mobius annulene was achieved [3].
