Infinitene might be aromatic

The infinity symbol–shaped molecule known as infinitene caught chemists’ attention in 2021. Calculations from a team at the University of Helsinki now suggest that the molecule might be aromatic after all (Phys. Chem. Chem. Phys. 2022, DOI: 10.1039/d2cp00637e).

Last year, a team at Nagoya University reported the successful synthesis of a looped benzocirculene made of 12 benzene rings fused into the shape of an infinity symbol or figure eight. C&EN readers voted infinitene the 2021 Molecule of the year (J. Am. Chem. Soc. 2022, DOI: 10.1021/jacs.1c10807).

When the Nagoya team reported their achievement, they calculated that the aromaticity was confined to individual rings rather than spread over the whole molecule. But Mesías Orozco-Ic, Rashid R. Valiev, and Dage Sundholm decided to run their own analysis. The shape of the new molecule is quite a challenge for calculating aromaticity. For example, its twisted form means that simple electron counting rules such as Hückel or Möbius aromaticity rules are not valid.

The Helsinki team used a quantum chemistry software package, Turbomole, to simulate infinitene’s response to an external magnetic field. Their calculations indicate that in a magnetic field, delocalized electrons would flow along the two edges of the molecule in two nonintersecting paths, a characteristic of aromatic molecules. As chemists synthesize more twisted structures, these sorts of calculations might uncover aromatic molecules that simple electron-counting rules miss.