(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) Å 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.