Infinitene

Infinitene is a chain of 12 fused benzene rings that forms an infinity symbol (∞) or, rotated 90°, a figure 8. After years of anticipation, it was synthesized in 2021 by Maciej Krzeszewski, Hideto Ito*, and Kenichiro Itami* at Nagoya University (Japan). Its official chemical name is in the fast facts table; but it is also known by the daunting term cyclo[c.c.c.c.c.c.e.e.e.e.e.e]dodecakisbenzene.

The structure of infinitene can also be thought of as two fused [6]helicene units. [6]Helicene is, of course, helical, and thus exists in two enantiomeric isomers with opposite chirality. To complete the infinitene loop, both helicenes must be of the same chirality, so that infinitene also exists in two enantiomers, designated as (+)-(P,P) and (–)-(M,M). The axial chirality symbols (P) and (M) stand for “plus”, or “right-handed”, and “minus”, or “left-handed”, respectively.

After synthesizing infinitene, Krzeszewski et al. performed all the necessary spectroscopic studies to confirm its structure. They also calculated the aromaticity of each benzene ring; but they did not report whether the entire molecule is aromatic. Subsequently, Mesías Orozco-Ic*, Rashid R. Valiev, and Dage Sundholm* at the University of Helsinki used sophisticated calculations to show that the molecule is aromatic; when an external magnetic field is applied, it creates two non-intersecting current density pathways along the molecules’ edges.

The synthesis of infinitene generated considerable buzz among chemists. C&EN readers, as well as other groups, voted it molecule of the year for 2021.