Abstract
The crystal structure of the title compound (4,17(20)-trans-pregnadiene-3,16-dione, C21H28O2) has been determined by direct methods using single-crystal X-ray diffraction data. The compound crystallizes into the orthorhombic space group P212121 with the unit cell parameters a = 7.908(2) A, b = 13.611(3) A, c = 16.309(4) A, and Z = 4. The structure has been refined to R = 0.058 for 3667 observed reflections. The bond distances and angles are in good agreement with guggulsterone E and other related steroid molecules. Ring A exists in the distorted sofa conformation, while rings B and C adopt the distorted chair conformation. Five-membered ring D is intermediate between the half-chair and envelope conformations. The A/B ring junction is quasi-trans, while ring systems B/C and C/D are trans fused about the C(8)–C(9) and C(13)–C(14) bonds, respectively. The steroid nucleus has a small twist, as shown by the C(19)–C(10)...C(13)–C(18) pseudo-torsion angle of 7.2°. The crystal structure is stabilized by intra-and intermolecular C-H...O hydrogen bonds.
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