Conformation of 17-Chloro-16-formylandrosta-5,16-dien-3β-yl acetate and 17-chloroandrosta-5,16-dien-3β-yl acetate

In the title compounds, C22H29ClO3, (I), and C21H29ClO2, (II), respectively, the B rings adopt a half-chair conformation and the D rings adopt an envelope conformation. A twist of the steroid skeleton of both compounds is observed. There is a positional disorder of the acetoxy group of (II), with the terminal atoms disordered over two positions with near equal occupancy. Quantum-mechanical ab initio calculations using a molecular orbital Hartree–Fock method were performed for the isolated molecules, thus allowing the distinction within the structural features of these two androstane derivatives of which characteristics are intrinsic to the molecules and which are due to packing effects. The skeletal twisting was found to be innate to the molecules, while the acetoxy disorder is due to packing effects.