Two (+)-α,4-dimethyl-2-oxocyclohexaneacetic acids: Hydrogen bonding in a terpenoid γ-keto acid and in a diastereomeric lactol

The (+)-(αS,1S,4R)-diastereomer of the title structure, C ₁₀H₁₆O₃, aggregates in the solid as non-symmetric dimers with disorder in both carboxyl groups [O⋯O = 2.710 (5) and 2.638 (5) Å]. The two molecules constituting the asymmetric unit pair around a pseudo-twofold rotational axis and differ only slightly in their distances and angles, but one methyl group displays rotational disorder absent in the other molecule. Five intermolecular C-H⋯O close contacts exist, involving both ketone groups. The (+)-(αR,1R,4R)-diastereomer exists in the crystal in its closed-ring lactol form, (3R,3aR,6R,7aR)-2,3,3a,4,5,6,7,7a- octahydro-7a-hydroxy-3,6-dimethylbenzo[b]furan-2-one, C₁₀H ₁₆O₃, and aggregates as hydrogen-bonded catemers that extend from the hydroxyl group of one molecule to the carbonyl group of a neighbor screw-related along b [O⋯O = 2.830 (3) Å and O-H⋯O = 169°]. One close intermolecular C-H⋯O contact exists involving the carbonyl group.