Is it possible to construct a three-dimensional shape that has only one side? In a manner of speaking, yes. To see how, cut a lengthwise strip off a piece of paper, loop it back on itself, but put a twist on half of it before closing the loop with some tape or staples. A computer-generated image of the mathematically equivalent object is shown in Figure 1.

For many years organic chemists have speculated about the possible synthesis of a molecule with this shape. Several examples have been produced, but none with a special property known as aromaticity.

Aromaticity, a term carried over from earlier years in chemistry when a frequent way to characterize compounds was by their smell, refers to a special stability conferred on molecules with a particular type of electron configuration. To the author's knowledge all aromatic molecules are necessarily cyclic (i.e. are shaped like a ring). In most molecules, a principle known as Hückel's Rule dictates that when the ring contains 4n + 2 pi-type¹ electrons, where n is a whole number (1, 2, 3...), the molecule is aromatic (read: especially stable). Benzene, a familiar molecule to chemistry students, is the simplest example of an aromatic species, with six pi-type electrons. Conversely, if the ring contains only 4n pi-type electrons, it is usually anti-aromatic, or especially unstable.

On the other hand, it has been previously postulated (on the basis of quantum mechnical models) that for a cyclic molecule in the shape of a Möbius strip, Hückel's Rule ought to be reversed - that is, a ring with 4n pi-type electrons should be especially stable. Past work involving transition state chemistry and short-lived ions seemed to confirm this hypothesis, but no stable aromatic Möbius species was produced.

In December of 2003 all that changed when Herges and colleagues from the Institut für Organische Chemie and the Max-Planck-Institut für Festkörperforschung published a scientific paper describing the synthesis of an aromatic Möbius molecule². It is stabilized by the presence of fused benzene rings and (in an oversimplification) contains a sum total of 24 pi-type electrons, which correponds to 4n (here, n equals six), just as expected.

Though perhaps only of academic interest, the whole story makes for fabulously twisted chemistry!

You can read the abstract of the paper here. Full-text access requires a subscription to Nature, which your school or college may have.