(6bR,10aS)-6b,10a-dimethyl-10,10a-dihydro-9H-fluoranthene

The crystal structure of the title compound, C18H20, contains molecules which are separated by normal van der Waals distances. The methyl groups attached at the junction of the acenaphthylene and cyclohexyl rings are cis with respect to each other. The naphthalene ring in the acenaphthylene moiety is essentially planar, with the remaining two C atoms lying 0.206 (6) and 0.253 (6) Angstrom on opposite sides of the plane of the naphthalene ring. The five-membered ring adopts an envelope conformation and the cyclohexyl ring is in a slightly flattened chair conformation. The molecular dimensions are as expected.