Structure of Equilenin at 100 K: an estrone-related steroid

The structure of the estrone-related steroid, Equilenin, C(18)H(18)O(2) (systematic name 3-hy­droxy-13-methyl-11,12,13,14,15,16-hexa­hydro­cyclo­penta­[a]phen­anthren-17-one), has been determined at 100 K. The crystals are ortho­rhom­bic, P2(1)2(1)2(1), and the absolute structure of the mol­ecule in the crystal has been determined by resonant scattering [Flack parameter = −0.05 (4)]. The C atoms of the A and B rings are almost coplanar, with an r.m.s. deviation from planarity of 0.0104 Å. The C ring has a sofa conformation, while the D ring has an envelope conformation with the methine C atom as the flap. The keto O atom and the methyl group are translated 0.78 and 0.79 Å, respectively, from the equivalent positions on 17β-estrone. In the crystal, mol­ecules are linked by O—H⋯O hydrogen bonds, forming chains parallel to the c-axis direction.