Case No. 104 · the exotic forty · have you seen this molecule?

Cyclo[18]carbon

a ring of pure carbon

File sealed

The detectives are still writing this one up. The poster and the facts are below; the film and the interrogation room open soon.

Booking photographs

Cyclo[18]carbon, front view, against a height chart in nanometers — FRONT

Cyclo[18]carbon, side view — SIDE · CID 14940714

The suspect, from its real atomic coordinates. Drag to turn it. Height chart in nanometers, ruled every 0.05 nm. The hole in a wedding ring is about 24 million times wider.

Rap sheet

Answers to: C18. Pure carbon, like diamond, but one ring of it.
Height: 0.72 nm, standing on its rim. Side on, a line.
Weight: 0.36 zeptograms
Bonds: Nine triples, nine singles. Most DFT bet on all doubles.
Marks: Doubly aromatic, as Hoffmann predicted in 1966.
Habits: Restless on salt. Past 1.5 volts it bolts or bonds to a neighbor.
Relatives: A C48 cousin survives in solution, threaded through three rings.
First seen: As a mass-spectrometer peak, flashed out of a precursor, in 1989.
Last seen: On salt at 5 kelvin near Zurich, pinned by its six former bromines.

atoms in it, every one of them carbon. Nothing else.
You’ve never seen one.

CASE FILE: Kaiser, K. et al. (2019) An sp-hybridized molecular carbon allotrope, cyclo[18]carbon. Science 365, 1299–1301.

The poster on the street

This is the photocopied wanted poster for Cyclo[18]carbon, No. 104 of the exotic forty. They were made for noticeboards around Boston, Cambridge and the rest of the east coast.

Found one? Scan its QR code with your phone. If you're a signed-in player, the sighting goes on your record with +1 XP.

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