(+/-)-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.