16 alpha,17 alpha-Epoxy-20-oxopregn-5-en-3 beta-yl acetate

The title compound, C23H32O4, has a 3 beta configuration, with the epoxy O atom at 16 alpha ,17 alpha. Rings A and C have slightly distorted chair con formations. Because of the presence of the C5=C6 double bond, ring B assume s an 8 beta ,9 alpha -half-chair conformation slightly distorted towards an 8 beta -sofa. Ring D has a conformation close to a 14 alpha -envelope. The acetoxy and acetyl substituents are twisted with respect to the average mo lecular plane of the steroid. The conformation of the molecule is compared with that given by a quantum chemistry calculation using the RHF-AM1 (RHF = Roothaan Hartree- Fock) Hamiltonian model. Cohesion of the crystal can be attributed to van der Waals interactions and weak intermolecular C-H . . .O interactions, which link the molecules head-to-tail along [101].