Fullerenes such as buckminsterfullerene (C60) and rugbyballene (C70) are common in sooting hydrocarbon flames, in the interstellar medium, and in meteorites such as in Murchison, but their fundamental gas phase formation mechanisms are rather elusive. Here, we reveal that the critical building block of fullerenes – the C40 nanobowl (C40H10) – can be prepared in the gas phase from corannulene (C20H10) via ring annulation to pentabenzocorannulene (C40H20) followed by successive cyclodehydrogenation. Exploiting benzocorannulene acts as a model system of annulation, an extensive theoretical treatment allowed us to expand the benzannulation mechanism through five sequential hydrogen abstraction – vinylacetylene addition (HAVA) stages to ultimately produce pentabenzocorannulene (C40H20), which in turn can be subjected to consecutive hydrogen abstraction – cyclodehydrogenation steps involving five-membered ring closures in the bay regions favorable at high temperatures typical for combustion flames or circumstellar envelopes. This five-step hydrogen abstraction – cyclodehydrogenation series leads from pentabenzo-corannulene (C40H20) to the C40 nano bowl (C40H10), which is considered an important molecular building block of fullerenes and an end-cap in the synthetic design of nanotubes. The proposed mechanism is anticipated to be versatile in the formation and growth of carbonaceous nanoparticles including buckyballs and carbon nanotubes in combustion systems and in deep space.

Toward the gas phase synthesis of nano bowl-40 (C40H10) through benzannulation of corannulene (C20H10)

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