(–)-2-(1,2,3,4,4a,5,6,7,8,8aα-Decahydro-4aβ,8α-dimethyl-7-oxo-2β-naphthyl)propionic acid: catemeric hydrogen bonding in a bicyclic sesquiterpenoid ζ-keto acid

In the title compound, C₁₅H₂₄O₃, derived from a naturally occurring sesquiterpenoid, the asymmetric unit consists of two mol­ecules differing by 167.4 (8)° in the rotational conformation of the carboxyl group. Each molecule aggregates separately with its own type as carboxyl-to-ketone hydrogen-bonding catemers [O⋯O = 2.715 (6) and 2.772 (6) Å, and O—H⋯O = 169 and 168°]. This generates two crystallographically independent single-strand hydrogen-bonding helices passing through the cell in the b direction, with opposite end-to-end orientations. One intermolecular C—H⋯O=C close contact exists for the carboxyl group of one of the mol­ecules. The structure is isostructural with that of a closely related unsaturated keto acid reported previously.