Dehydro­abietic acid

THE TITLE COMPOUND [SYSTEMATIC NAME: (1R,4aS,10aR)-7-iso-prop-yl-1,4a-dimethyl-1,2,3,4,4a,9,10,10a-octa-hydro-phen-anthrene-1-carboxylic acid], C(20)H(28)O(2), has been isolated from disproportionated rosin which is obtained by isomerizing gum rosin with a Pd-C catalyst.. Two crystallographically independent mol-ecules exist in the asymmetric unit. In each mol-ecule, there are three six-membered rings, which adopt planar, half-chair and chair conformations. The two cyclo-hexane rings form a trans ring junction with the two methyl groups in axial positions. The crystal structure is stabilized by inter-molecular O-H⋯O hydrogen bonds.