(±)-trans-3-Oxo-1,2,3,4,4a,9,10,10a-octahydrophenanthrene-10a-carboxylic acid: catemeric hydrogen bonding in a δ-keto acid

The title compound, C15H16O3, aggregates as hydrogen-bonded catemers progressing from each carboxyl to the ketone of a screw-related neighbor [O⋯O = 2.6675 (14) Å and O—H⋯O = 170°]. Two parallel centrosymmetrically related single-strand hydrogen-bonding helices proceed through the cell in the b-axis direction. The packing includes three intermolecular C—H⋯O=C close contacts, involving both the ketone and the carboxyl group. The structure is isomorphous with that of the previously described Δ4 α,β-unsaturated ketone.

The title compound, C 15 H 16 O 3 , aggregates as hydrogenbonded catemers progressing from each carboxyl to the ketone of a screw-related neighbor [OÁ Á ÁO = 2.6675 (14) Å and O-HÁ Á ÁO = 170 ]. Two parallel centrosymmetrically related single-strand hydrogen-bonding helices proceed through the cell in the b-axis direction. The packing includes three intermolecular C-HÁ Á ÁO C close contacts, involving both the ketone and the carboxyl group. The structure is isomorphous with that of the previously described Á 4 ,unsaturated ketone.
Keto acids with few fully rotatable bonds thus display an increased tendency to form acid-to-ketone H-bonding chains. In this context, we describe the title compound (I), which aggregates in the less common catemer mode.   (Table 1) 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 O in terms of its deviation from, respectively, C=O axiality and planarity with the carbonyl. In (I) these angles are 117° for H···O=C and -6.5° for H···O=C-C, extremely close to the "ideal" angles of 120 and 0°.
Within the 2.6 Å range we survey (Steiner, 1997), three intermolecular C-H···O=C close contacts were found in the packing, involving both the ketone and the carboxyl group. (Table 1).
Compound (I) is derived from the Δ 4 isoskeletal unsaturated keto acid whose structure we have previously reported (Miller et al., 1999), and the molecular shapes of these two compounds are so similar that (I) was found to be isomorphous with the prior material.
Experimental 1-Tetralone was carbomethoxylated and then subjected to Robinson annulation as described by Thompson & McPherson (1977). The resulting unsaturated keto ester was hydrogenated over a Pd/C catalyst, after which Jones oxidation was employed to correct for overreduction. Mild saponification, modeled on that described by Thompson & Shah (1983), provided (I), which was sublimed and crystallized from diethyl ether to give the crystal used, m.p. 460 K. The solid-state (KBr) supplementary materials sup-2 infrared spectrum of (I) has C=O absorptions at 1716 & 1685 cm -1 . This peak separation is typical of the H-bonding shifts in catemers, due to, respectively, its removal from the acid C=O and its addition to the ketone. In CHCl 3 solution, where dimers predominate, these peaks coalesce to a single absorption at 1707 cm -1 .