5-Oxocyclooctanecarboxylic acid: hydrogen-bonding pattern and conformational disorder in a medium-ring varepsilon-keto acid

Molecules of the title compound, C(9)H(14)O(3), adopt a chiral 'boat-chair' conformation, in which the carboxyl group avoids potential cross-ring ketone interactions by an outward 'equatorial' orientation. The asymmetric unit contains two such molecules, one conformationally fixed without disorder, (I), and the other, (I'), extensively disordered, both in the bond lengths and angles of the carboxyl and by a coupled 'up-down' conformational disordering [ratio of 60:40 (1)] of the remote ends of the boat-chair system. Each molecule in the asymmetric unit forms a centrosymmetric hydrogen-bonded carboxyl dimer with a second molecule of its own type. For (I), O.O = 2.658 (3) A and O-H.O = 174 degrees. For (I'), O.O = 2.653 (3) A and O-H.O = 165 degrees. A number of intermolecular C=O.H-C close contacts are found.

Phenyl- and mesitylglyoxylic acids: catemeric hydrogen bonding in two alpha-keto acids

alpha-Oxobenzeneacetic (phenylglyoxylic) acid, C(8)H(6)O(3), adopts a transoid dicarbonyl conformation in the solid state, with the carboxyl group rotated 44.4 (1) degrees from the nearly planar benzoyl moiety. The heterochiral acid-to-ketone catemers [O.O = 2. 686 (3) and H.O = 1.78 (4) A] have a second, longer, intermolecular O-H.O contact to a carboxyl sp(3) O atom [O.O = 3.274 (2) and H.O = 2.72 (4) A], with each flat ribbon-like chain lying in the bc plane and extending in the c direction. In alpha-oxo-2,4, 6-trimethylbenzeneacetic (mesitylglyoxylic) acid, C(11)H(12)O(3), the ketone is rotated 49.1 (7) degrees from planarity with the aryl ring and the carboxyl group is rotated a further 31.2 (7) degrees from the ketone plane. The solid consists of chiral conformers of a single handedness, aggregating in hydrogen-bonding chains whose units are related by a 3(1) screw axis, producing hydrogen-bonding helices that extend in the c direction. The hydrogen bonding is of the acid-to-acid type [O.O = 2.709 (6) and H.O = 1.87 (5) A] and does not formally involve the ketone; however, the ketone O atom in the acceptor molecule has a close polar contact with the same donor carboxyl group [O.O = 3.005 (6) and H.O = 2.50 (5) A]. This secondary hydrogen bond is probably a major factor in stabilizing the observed cisoid dicarbonyl conformation. Several intermolecular C-H.O close contacts were found for the latter compound.