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Acenaphthene is a polycyclic aromatic hydrocarbon (PAH) consisting of naphthalene with an ethylene bridge connecting positions 1 and 8.
A 1229 (OTTO) Acenaphthene, 96% Cas 83-32-9 - used on a large scale to prepare naphthalene dicarboxylic anhydride, which is a precursor to dyes and optical brighteners.