(+)-23,24-Dinor-3 alpha,9 alpha-epoxy-11-oxo-5 beta-cholan-22-oic acid: mutual carboxyl-to-ether dimeric hydrogen bonding in a steroidal carboxy-ketoether

The title steroidal carboxy-keto ether, C22H32O4, forms non-centrosymmetric dimers involving two distinct carboxyl-to-ether hydrogen bonds [O ... O = 2.718(3) and 2.701(3)Angstrom], in which the ketone does not participate. T he asymmetric unit is the dimer, whose two molecules are conformationally d istinct. The principal conformational difference between the two molecules lies in the carboxyl-group rotation which differs by 28.2(5)degrees. The C= O oxygen of one of the carboxyl groups shows unusual anisotropy, attributed to thermal motion associated with a packing cavity surrounding that carbox yl group but absent in the other. Several C-H ... O close contacts are pres ent.