Acta Cryst. (2006). E62, o2120-o2122  [ doi:10.1107/S160053680601405X ]

(-)-Isosantonic acid: alteration of the hydrogen-bonding mode by configurational inversion at a single centre in a ,-diketocarboxylic acid

J. Zinczuk, E. A. Ruveda, R. A. Lalancette and H. W. Thompson

Abstract: The title diketo acid, (1R,3aS,6aS,7R,9S)-(-)-,3a,7-trimethyl-5,8-dioxo-1,4-ethanoperhydropentalene-1-acetic acid (C₁₅H₂₀O₄), is shown to aggregate in the crystal structure as acid-to-ketone hydrogen-bonding catemers, whose chains follow 2₁ screw axes from each carboxyl to a ketone in a neighbouring molecule [OO = 2.7472 (13) Å and OH-O = 172.7 (17)°]. Two parallel counterdirectional screw-related single-strand hydrogen-bonding chains pass through the cell in the a direction. Six intermolecular C-HO=C close contacts are found. Comparisons are drawn with a diastereomer having the opposite configuration at the methylated chiral centre adjacent to the carboxyl group.

Online 5 May 2006

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