(±)-trans-3-Benzoyl­bicyclo­[2.2.2]octane-2-carboxylic acid

Roger A Lalancette; Hugh W Thompson; Andrew P J Brunskill

doi:10.1107/S1600536808024112

. 2008 Aug 6;64(Pt 9):o1664. doi: 10.1107/S1600536808024112

(±)-trans-3-Benzoylbicyclo[2.2.2]octane-2-carboxylic acid

Roger A Lalancette ^a, Hugh W Thompson ^a, Andrew P J Brunskill ^a,^*

PMCID: PMC2960648 PMID: 21201657

Abstract

The title keto acid, C₁₆H₁₈O₃, displays significant twisting of all three ethylene bridges in its bicyclo[2.2.2]octane structure owing to steric interactions; the bridgehead-to-bridgehead torsion angles are 13.14 (12), 13.14 (13) and 9.37 (13)°. The compound crystallizes as centrosymmetric carboxyl dimers [O⋯O = 2.6513 (12) Å and O—H⋯O = 178°], which have two orientations within the cell and contain no significant carboxyl disorder.

Related literature

For related literature, see: Blackstock et al. (1987 ▶); Deutsch (1972 ▶); Scribner & Miller (1965 ▶); Zimmerman et al. (1992 ▶).

Experimental

Crystal data

C₁₆H₁₈O₃
M _r = 258.30
Monoclinic,
a = 7.9155 (7) Å
b = 11.1129 (9) Å
c = 14.7559 (12) Å
β = 93.882 (3)°
V = 1295.01 (19) Å³
Z = 4
Cu Kα radiation
μ = 0.73 mm⁻¹
T = 100 (2) K
0.49 × 0.30 × 0.17 mm

Data collection

Bruker SMART CCD APEXII area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2001 ▶) T _min = 0.716, T _max = 0.886
7983 measured reflections
2405 independent reflections
2350 reflections with I > 2σ(I)
R _int = 0.029

Refinement

R[F ² > 2σ(F ²)] = 0.038
wR(F ²) = 0.100
S = 1.03
2405 reflections
174 parameters
H-atom parameters constrained
Δρ_max = 0.33 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Data collection: APEX2 (Bruker, 2006 ▶); cell refinement: APEX2; data reduction: SAINT (Bruker, 2005 ▶); program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808024112/fl2213sup1.cif

e-64-o1664-sup1.cif^{(18.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808024112/fl2213Isup2.hkl

e-64-o1664-Isup2.hkl^{(118.2KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3⋯O2ⁱ	0.84	1.81	2.6513 (12)	178

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Symmetry code: (i) Inline graphic .

Acknowledgments

HWT is grateful to Professor Gree Loober Spoog for helpful consultations. The authors acknowledge support by NSF–CRIF grant No. 0443538.

supplementary crystallographic information

Comment

Our study of crystalline keto acids concerns their repertoire of five known H-bonding modes. Two of these lack ketone involvement, including the commonest, acid dimerization, which is found in the aggregation of the title compound (I).

Fig. 1 shows the asymmetric unit of (I) with its numbering. Even simple bicyclo[2.2.2]octane systems often adopt a twist about the threefold axis, presumably to relieve eclipsing strain in their ethylene bridges (Deutsch, 1972; Blackstock et al., 1987; Zimmerman et al., 1992). In (I) that strain is supplemented by more serious eclipsing and 1,3-diaxial interactions involving the substituents, so that all three bridges are significantly twisted. Fig. 1 illustrates the extent to which the C5—C6 ethylene bridge is clearly not parallel to the others; however, the appearance of parallelism in the C2—C3 and C7—C8 bridges is an artifact of the viewing angle. The torsion angles for the three bridges are: C1—C2—C3—C4 = 13.14 (12)°, C1—C6—C5—C4 = 13.14 (13)°, C1—C7—C8—C4 = 9.37 (13)°.

The benzoyl group has component parts that are only approximately coplanar [the dihedral angle for C3—C10—C11—O1 versus the aromatic ring = 24.60 (7)°], and is oriented so that the ketone C=O is aimed toward C2. The carboxyl group is turned, with its C=O toward C3, so that the O2—C9—C2—C3 torsion angle is 18.76 (15)°. The dihedral angle between the ketone (C3—C10—C11—O1) and carboxyl group (C2—C9—O2—O3) is 79.80 (4)°. One may envision other possible conformations for the phenyl ring; however, because of steric hindrance, there is very little rotational freedom for the phenyl group here.

Although carboxyl dimers frequently display complete or partial averaging of C—O bond lengths and C—C—O angles due to disorder, no significant averaging is observed in (I), where these lengths and angles are similar to those in other highly ordered dimeric carboxyls.

Fig. 2 shows the packing for (I), typical for racemic keto acids that are dimeric. Centrosymmetric dimers are centered at 1/2,1/2,1/2 in the chosen cell, with a second screw-related set centered on the a cell edge. No close intermolecular contacts were found within the 2.6 Å range we routinely survey for non-bonded C—H···O packing interactions.

Experimental

endo-Bicyclo[2.2.2]oct-5-ene-2,3-dicarboxylic anhydride, purchased from Aldrich Chemical Co., Milwaukee, Wisconsin, USA, was hydrogenated under typical conditions (atmospheric pressure, room temperature, 5%Pd/C, EtOAc) and the isolated product used directly in a Friedel-Crafts acylation of benzene (AlCl₃). The cis keto acid initially obtained (mp 446 K) was epimerized by refluxing in excess aqueous KOH (Scribner & Miller, 1965). The isolated trans product (I) was vacuum-distilled and crystallized from acetonitrile to give the crystal used, mp 444 K.

The solid-state IR spectrum (KBr) of (I) has C=O absorptions at 1692 (acid) and 1677 cm^-1 (ketone), normal for dimerized COOH and for a benzoyl group without H bonding but with significant coplanarity. In CHCl₃ solution these peaks appear at 1702 & 1679 cm^-1.