Nature Chem. http://doi.org/s7t (2014)

Credit: © 2014 NPG

You name it, they'll synthesize it: organic chemists are adept at producing the most amazing and challenging molecules.

Synthesizing Möbius annulenes — completely conjugated cyclic hydrocarbons with the geometry of a Möbius strip — is a continuing challenge. Gaston Schaller and colleagues have now found a route for preparing multiply twisted annulenes. Inspired by the notion that twisted structures often wind around themselves to release strain — think of a twisted telephone cord that got all wound up — they set out to synthesize a triply twisted Möbius molecule featuring three loops (pictured), which should be more stable than the loop-free variant.

The net amount of overlap induced by the loops can be quantified by a parameter known as writhe; likewise, the degree of twistedness is quantifiable. According to the Călugăreanu theorem, the sum of writhe and twist is constant throughout topological transformations (stretching, compressing or bending). In other words, a shape can convert twist into writhe by making loops.

The authors chose precursors that have the right writhe, and at the end of a chain of reactions that took several weeks to complete, obtained the desired [24]dehydroannulene.