Mark Davison

3-Oxo-5β-24-norcholanic acid: acid-to-acid hydrogen-bonding catemers employing the rare anti carboxyl conformation in the aggregation of a steroid keto acid

The title ketocarboxylic acid [systematic name: (5R,8R,9S,10S,13R,14S,17R,20R)-3-oxo-24-norcholanic acid], C(23)H(36)O(3), forms acid-to-acid hydrogen-bonding chains [O...O = 2.620 (2) A and O-H...O = 163 (3) degrees ] in which all carboxyl groups adopt the rare anti conformation, while the ketone group does not participate in the hydrogen bonding. The occurrence and energetics of this conformation are discussed. One intermolecular C-H...O close contact exists, which plays a role in stabilizing the hydrogen-bonding arrangement.

Two (+)-α,4-dimethyl-2-oxocyclohexaneacetic acids: hydrogen bonding in a terpenoid γ-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.

(+/-)-7-oxo-1,2,3,4,4a,5,6,7-octahydronaphthalene-1-acetic acid: catemeric hydrogen bonding and diastereomeric disorder in a bicyclic unsaturated epsilon-keto acid.

The 68.5:31.5 mixture of diastereoisomers obtained in the synthesis of the title compound, C(12)H(16)O(3), yielded sharply melting crystals containing the same ratio of epimers, in a disordered crystallographic arrangement. The disorder resides almost entirely in the carboxymethyl side chain, but places the two sets of carboxyl O atoms at nearly identical paired spatial positions. Neither component displays significant carboxyl disorder, and the molecules aggregate as hydrogen-bonded carboxyl-to-ketone catemers [O.O = 2.673 (4) A and O-H.O = 158 degrees ] having glide-related components, with centrosymmetrically related pairs of chains following axes perpendicular to b. Close intermolecular C-H.O contacts exist for both the ketone and the carboxyl group. The energetics of the epimers and of their crystallization mode are discussed.

(+/-)-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.

(2SR,4aSR,8aSR)-6-Oxoperhydro­naphthalene-2-carboxylic acid

In the title racemic compound, C11H16O3, the molecule adopts a conformation that places its carboxyl group in an equatorial position. Molecules aggregate by hydrogen-bond pairing of carboxyl groups, yielding centrosymmetric dimers that are arranged into layers in the (020) planes.

(±)-trans-3-Oxo-1,2,3,4,4a,9,10,10a-octa­hydro­phenanthrene-10a-carboxylic acid: catemeric hydrogen bonding in a δ-keto acid

The title compound, C15H16O3, aggregates as hydrogen-bonded catemers progressing from each carboxyl to the ketone of a screw-related neighbor [O⋯O = 2.6675 (14) Å and O—H⋯O = 170°]. Two parallel centrosymmetrically related single-strand hydrogen-bonding helices proceed through the cell in the b-axis direction. The packing includes three intermolecular C—H⋯O=C close contacts, involving both the ketone and the carboxyl group. The structure is isomorphous with that of the previously described Δ4 α,β-unsaturated ketone.

Formation of non-centrosymmetric dimers in (1S*,4aR*,8aR*)-deca­hydro­naphthalene-1-carboxyl­ic acid

The all-cis racemate of the title compound, C11H18O2, crystallizes in the chair-chair conformation that places the carboxyl group in an equatorial postion. The space group is centrosymmetric but the compound aggregates as dimers whose components are related by a C2 axis [O⋯O = 2.665 (3) A and O—H⋯O = 177°]. In the crystal structure, one C—H⋯O=C close contact is found.