​ACENAPHTHENE, C₁₂H₁₀, a hydrocarbon isolated from the fraction of coal-tar boiling at 260°–270° by M. P. E. Berthelot, who, in conjunction with Bardy, afterwards synthesized it from α-ethyl naphthalene (Ann. Chem. Phys., 1873, vol. xxix.). It forms white needles (from alcohol), melts at 95° and boils at 278°. Oxidation gives naphthalic acid (1.8 naphthalene dicarboxylic acid).

Acenaphthalene, C₁₂H₈, a hydrocarbon crystallizing in yellow tables and obtained by passing the vapour of acenaphthene over heated litharge. Sodium amalgam reduces it to acenaphthene; chromic acid oxidizes it to naphthalic acid.