(-)-3,7-Dioxo-5beta-cholanic acid: dual hydrogen-bonding modes in a diketonic bile-acid derivative.

The asymmetric unit of the title compound, C(24)H(36)O(4), contains three molecules, all differing in their side-chain conformations and all linked by hydrogen bonding confined entirely within a three-molecule block. One connection is of the acid-to-ketone type [O...O = 2.7055 (19) Angstrom and O-H...O = 180 degrees ] and the other involves carboxyl pairing [O...O = 2.6485 (18) and 2.6598 (18) Angstrom, and O-H...O = 168 and 174 degrees ]. Numerous intermolecular C-H...O close contacts connect neighbouring molecules.

(+)-3,11-Dioxo-5alpha-androstanecarboxylic acid: catemeric hydrogen bonding in a steroidal diketo acid.

The title compound, C(20)H(28)O(4), aggregates catemerically, with hydrogen-bonding links from each carboxylic acid group to the 3-oxo group in the A ring of a molecule translationally related in both the a and the b directions [O...O = 2.7537 (18) Angstrom and O-H...O = 162 degrees ]. The 11-oxo group in the C ring is not involved in the hydrogen bonding. A single intermolecular C-H...O close contact connects the carboxyl C=O group to a methyl group on an adjacent molecule.

Two (+)-alpha,4-dimethyl-2-oxocyclohexaneacetic acids: hydrogen bonding in a terpenoid gamma-keto acid and in a diastereomeric lactol.

The (+)-(alphaS,1S,4R)-diastereomer of the title structure, C10H16O3, aggregates in the solid as non-symmetric dimers with disorder in both carboxyl groups [O...O = 2.710 (5) and 2.638 (5) A]. The two molecules constituting the asymmetric unit pair around a pseudo-twofold rotational axis and differ only slightly in their distances and angles, but one methyl group displays rotational disorder absent in the other molecule. Five intermolecular C-H...O close contacts exist, involving both ketone groups. The (+)-(alphaR,1R,4R)-diastereomer exists in the crystal in its closed-ring lactol form, (3R,3aR,6R,7aR)-2,3,3a,4,5,6,7,7a-octahydro-7a-hydroxy-3,6-dimethylbenzo[b]furan-2-one, C(10)H(16)O(3), and aggregates as hydrogen-bonded catemers that extend from the hydroxyl group of one molecule to the carbonyl group of a neighbor screw-related along b [O...O = 2.830 (3) A and O-H...O = 169 degrees]. One close intermolecular C-H...O contact exists involving the carbonyl group.

(+/-)-3-Ethyl-2-methyl-4-oxocyclohexanecarboxylic acid: catemeric hydrogen bonding in a cyclic delta-keto acid.

In the title compound, C(10)H(16)O(3), the two molecules of the asymmetric unit form acid-to-ketone hydrogen-bonded chains. The two species differ only very slightly and are related by a pseudo-center, so that the apparent translational relationship among the units of the hydrogen-bonded chain is actually a pseudo-translation, with the molecules alternating in type. Two counterdirectional pairs of chains proceed through each cell [O.O = 2.743 (2) and 2.683 (2) A, and O-H.O = 171 (3) and 157 (3) degrees ]. Three intermolecular C-H.O close contacts were found, involving all three O atoms of one of the molecules.