(±)-2-Oxocyclo-penta-neacetic acid: catemeric hydrogen bonding in a γ-keto acid.

The title racemate, C(7)H(10)O(3), aggregates in the solid as acid-to-ketone hydrogen-bonding catemers [O⋯O = 2.7050 (13) Å and O-H⋯O = 166.1 (17)°] having glide-related components.

The epimeric 9-oxobicyclo[3.3.1]nonane-3-carboxylic acids: hydrogen-bonding patterns of the endo acid and the lactol of the exo acid.

The two delta-keto carboxylic acids of the title, both C(10)H(14)O(3), are epimeric at the site of carboxyl attachment. The endo (3alpha) epimer, (I), has its keto-acid ring in a boat conformation, with the tilt of the carboxyl group creating conformational chirality. The molecules form hydrogen bonds by centrosymmetric pairing of carboxyl groups across the corners of the chosen cell [O.

(+-)-12-Oxotricyclo[6.2.2.0(1,6)]dodecane-10-carboxylic acid: hydrogen bonding in a tricyclic delta-keto acid.

The ring system of the title compound, C(13)H(18)O(3), was synthesized by addition of ethyl acrylate to the dienamine of 2-octalone. The keto acid aggregates in the solid as acid-to-acid dimers [O..

1'-Acetylferrocene-1-carboxylic acid: an instance of hydrogen bonding in the rare dimeric acid-to-ketone mode.

The title compound, [Fe(C(6)H(5)O(2))(C(7)H(7)O)], adopts a conformation involving partial staggering of its rings and aggregates in the solid as acid-to-ketone hydrogen-bonding dimers [O.O = 2.720(4)A and O-H.