Unconventional Pathway in the Gas‐Phase Synthesis of 9H‐Fluorene (C13H10) via the Radical–Radical Reaction of Benzyl (C7H7) with Phenyl (C6H5).

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five‐membered ring—9H‐fluorene (C13H10)—is produced isomer‐specifically in the gas phase by reacting benzyl (C7H7⋅) with phenyl (C6H5⋅) radicals in a pyrolytic reactor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by theoretical calculations, which first produces diphenylmethane and unexpected 1‐(6‐methylenecyclohexa‐2,4‐dienyl)benzene intermediates (C13H12) accessed via addition of the phenyl radical to the ortho position of the benzyl radical. These findings offer convincing evidence for molecular mass growth processes defying conventional wisdom that radical‐radical reactions are initiated through recombination at their radical centers. The structure of 9H‐fluorene acts as a molecular building block for complex curved nanostructures like fullerenes and nanobowls providing fundamental insights into the hydrocarbon evolution in high temperature settings. [ABSTRACT FROM AUTHOR]