trans-4-Acetylcyclohexanecarboxylic acid and (+/-)-trans-2-acetylcyclohexanecarboxylic acid: hydrogen-bonding patterns in two isomeric keto acids.

Both title compounds, C(9)H(14)O(3), display carboxyl-dimer hydrogen-bonding patterns. The 4-acetyl isomer adopts a chiral conformation with negligible disordering of the methyl and carboxyl groups and forms centrosymmetric dimers across the b and c edges of the chosen cell [O.O = 2.667 (3) A and O-H.O = 175 degrees ]. Intermolecular C-H.O close contacts were found for both carbonyl groups. In the 2-acetyl isomer, there is no intramolecular interaction between the carboxyl and acetyl groups and the hydrogen bonding involves centrosymmetric carboxyl dimerization across the ab and ac faces of the chosen cell [O.O = 2.668 (2) A and O-H.O = 173 degrees ]. The carboxyl group is negligibly disordered, but significant rotational disordering was found for the acetyl methyl group. An intermolecular C-H.O close contact was found involving the ketone group.