Unconventional Pathway in the Gas-Phase Synthesis of 9H-Fluorene (C 13 H 10 ) via the Radical-Radical Reaction of Benzyl (C 7 H 7 ) with Phenyl (C 6 H 5 ).

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five-membered ring-9H-fluorene (C ₁₃ H ₁₀ )-is produced isomer-specifically in the gas phase by reacting benzyl (C ₇ H ₇ ⋅) with phenyl (C ₆ H ₅ ⋅) 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 (C ₁₃ H ₁₂ ) 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.
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