Dehydroabietic acid

The title compound [systematic name: (1R,4aS,10aR)-7-isopropyl-1,4a-dimethyl-1,2,3,4,4a,9,10,10a-octahydrophenanthrene-1-carboxylic acid], C20H28O2, has been isolated from disproportionated rosin which is obtained by isomerizing gum rosin with a Pd-C catalyst.. Two crystallographically independent molecules exist in the asymmetric unit. In each molecule, there are three six-membered rings, which adopt planar, half-chair and chair conformations. The two cyclohexane rings form a trans ring junction with the two methyl groups in axial positions. The crystal structure is stabilized by intermolecular O—H⋯O hydrogen bonds.

2009). Dehydroabietic acid is also widely used as starting material for design and synthesis of biological compounds (Sepulveda et al., 2005;Rao, Song & He, 2008;Rao, Song He & Jia, 2008;Wada et al., 1985). In this work, we describe the crystal structure of the title compound.
The overall geometry of the title compound ( Fig. 1) is comparable to that found for dehydroabietic N-methyl anilide (Rao et al., 2006) Two crystallorgraphic independent molecules exist in the asymmetric unit. In each molecule there are three six-membered rings, in which they form plannar, half-chair and chair conformations, respectively. The tricyclo phenanthrene structure of the title compound exhibited the same conformation with dehydroabietic N-methyl anilide. The two cyclohexane rings form a trans ring junction with two methyl groups in the same side of tricyclo phenanthrene structure. There are three chiral centers in each molecule, they exhibited R-, S-and R-configurations, respectively.
The crystal structure is stabilized by intermolecular O-H···O hydrogen bonds.

Experimental
The title compound wasere isolated from disproportionated rosin by recrystallization 5 times from acetone. Single crystals were grown from acetone.

Refinement
H atoms were positioned geometrically and refined as riding atoms, with C-H = 0.96Å and U iso (H) = 1.5U eq (C) for methyl H atoms, and C-H = 0.97-0.98Å and U iso (H) = 1.2U eq (C) for all other H atoms. Fig. 1  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.