Gas-Phase Synthesis of the Elusive Cyclooctatetraenyl Radical (C₈H₇) via Triplet Aromatic Cyclooctatetraene (C₈H₈) and Non-Aromatic Cyclooctatriene (C₈H₈) Intermediates

The 1,2,4,7-cyclooctatetraenyl radical (C₈H₇) has been synthesized for the very first time via the bimolecular gas-phase reaction of ground-state carbon atoms with 1,3,5-cycloheptatriene (C₇H₈) on the triplet surface under single-collision conditions. The barrier-less route to the cyclic 1,2,4,7-cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non-aromatic 2,4,6-cyclooctatriene (C₈H₈) and the triplet aromatic 1,3,5,7-cyclooctatetraene (C₈H₈). Our approach provides a clean gas-phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7-cyclooctatetraenyl via a single-collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods.