(2RS,8aRS)-6-Oxo-1,2,3,4,6,7,8,8a-octahydronaphthalene-2-carboxylic acid

The title racemate, C11H14O3, aggregates in the crystal structure as acid-to-ketone O—H⋯O hydrogen-bonding catemers whose components are glide-related. The relative stereochemistry at the carboxyl group arises spontaneously during the synthesis. Two intermolecular C—H⋯O=C close contacts were found, both involving the acid group.

The title racemate, C 11 H 14 O 3 , aggregates in the crystal structure as acid-to-ketone O-HÁ Á ÁO hydrogen-bonding catemers whose components are glide-related. The relative stereochemistry at the carboxyl group arises spontaneously during the synthesis. Two intermolecular C-HÁ Á ÁO C close contacts were found, both involving the acid group.
The disordering of C-O bond lengths and C-C-O angles often seen in carboxyl dimers becomes impossible when the H-bonding mode precludes the required averaging mechanisms. Because (I) is not dimeric the distances and angles here are fully ordered and thus typical of those in highly ordered dimeric carboxyls (Borthwick, 1980). Each carboxylic acid is linked to the ketone in a molecule glide related in the c direction. Glide relationships for intra-chain units in catemers is far less common than screw-related schemes. Each of the four molecules in the chosen cell participates in a separate H-bonding chain and these pass through the cell in counterdirectional pairs related by centrosymmetry, with the chains advancing by one cell in a and one-half cell in c for each H bond.
We characterize the geometry of H bonding to carbonyls using a combination of the H···O=C angle and the H···O=C-C torsion angle. These describe the approach of the H atom to the receptor O in terms of its deviation from, respectively, C=O axiality (ideal = 120°) and planarity with the carbonyl (ideal = 0°). In (I), these angles are 131.0 (6) & 0.6 (8)°.
Within the 2.6 Å range we standardly survey for C-H···O packing interactions (Steiner, 1997), two intermolecular close contacts were found, both involving O2, the carboxyl carbonyl (see table). (1965); crystallization from ethyl acetate yielded material suitable for X-ray, mp 418 K. The C2/C8a stereochemistry clearly represents the stabler of the two epimers possible and probably arises as the result of equilibrations during the synthesis (House et al., 1965).

Compound (I) was synthesized by the method of Finnegan & Bachman
The solid-state (KBr) infrared spectrum of (I) has C=O absorptions at 1721 & 1640 cm -1 , with a peak separation typical of the shifts seen in catemers, due, respectively, to removal of H bonding from the acid C=O and addition of H bonding to the ketone; an alkene peak appears at 1616 cm -1 . In CHCl 3 solution, where dimers predominate, these bands appear, respectively, at 1708, 1666 and 1622 cm -1 .
supplementary materials sup-2 Refinement All H atoms for (I) were found in electron-density difference maps. The positional parameters for the carboxyl H were allowed to refine but the U iso (H) was held at 1.5U eq (O). The methylene, methine and vinyl Hs were placed in geometrically idealized positions and constrained to ride on their parent C atoms with C-H distances of 0.99, 1.00 & 0.95 Å, respectively, and U iso (H) = 1.2U eq (C). Fig. 1. The asymmetric unit of (I), with its numbering. Displacement ellipsoids are drawn at the 40% probability level. (2RS,8aRS)-6-Oxo-1,2,3,4,6,7,8,8a-octahydronaphthalene-2-carboxylic acid 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.