organic compounds
(±)-trans-3-Benzoylbicyclo[2.2.2]octane-2-carboxylic acid
aCarl A. Olson Memorial Laboratories, Department of Chemistry, Rutgers University, Newark, NJ 07102, USA
*Correspondence e-mail: rogerlal@andromeda.rutgers.edu
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
|
Refinement
|
Data collection: APEX2 (Bruker, 2006); cell 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.
Supporting information
10.1107/S1600536808024112/fl2213sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536808024112/fl2213Isup2.hkl
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.
All H atoms for (I) were found in electron density difference maps. The O—H was constrained to an idealized position with its distance fixed at 0.84 Å and Uiso(H) = 1.5Ueq(O). The methylene, methine and aromatic 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 and 0.95 Å, respectively, and Uiso(H) = 1.2Ueq(C).
Data collection: APEX2 (Bruker, 2006); cell
APEX2 (Bruker, 2006); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).C16H18O3 | F(000) = 552 |
Mr = 258.30 | Dx = 1.325 Mg m−3 |
Monoclinic, P21/c | Melting point: 444 K |
Hall symbol: -P 2ybc | Cu Kα radiation, λ = 1.54178 Å |
a = 7.9155 (7) Å | Cell parameters from 7078 reflections |
b = 11.1129 (9) Å | θ = 3.0–69.4° |
c = 14.7559 (12) Å | µ = 0.73 mm−1 |
β = 93.882 (3)° | T = 100 K |
V = 1295.01 (19) Å3 | Block, colourless |
Z = 4 | 0.49 × 0.30 × 0.17 mm |
Bruker SMART CCD APEXII area-detector diffractometer | 2405 independent reflections |
Radiation source: fine-focus sealed tube | 2350 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.029 |
ϕ and ω scans | θmax = 69.8°, θmin = 5.0° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | h = −8→9 |
Tmin = 0.716, Tmax = 0.886 | k = −13→11 |
7983 measured reflections | l = −16→17 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.038 | H-atom parameters constrained |
wR(F2) = 0.100 | w = 1/[σ2(Fo2) + (0.0502P)2 + 0.6168P] where P = (Fo2 + 2Fc2)/3 |
S = 1.03 | (Δ/σ)max < 0.001 |
2405 reflections | Δρmax = 0.33 e Å−3 |
174 parameters | Δρmin = −0.20 e Å−3 |
0 restraints | Extinction correction: SHELXTL (Sheldrick, 2004), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0033 (6) |
C16H18O3 | V = 1295.01 (19) Å3 |
Mr = 258.30 | Z = 4 |
Monoclinic, P21/c | Cu Kα radiation |
a = 7.9155 (7) Å | µ = 0.73 mm−1 |
b = 11.1129 (9) Å | T = 100 K |
c = 14.7559 (12) Å | 0.49 × 0.30 × 0.17 mm |
β = 93.882 (3)° |
Bruker SMART CCD APEXII area-detector diffractometer | 2405 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | 2350 reflections with I > 2σ(I) |
Tmin = 0.716, Tmax = 0.886 | Rint = 0.029 |
7983 measured reflections |
R[F2 > 2σ(F2)] = 0.038 | 0 restraints |
wR(F2) = 0.100 | H-atom parameters constrained |
S = 1.03 | Δρmax = 0.33 e Å−3 |
2405 reflections | Δρmin = −0.20 e Å−3 |
174 parameters |
Experimental. crystal mounted on cryoloop using Paratone-N |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.61369 (11) | 0.84095 (8) | 0.26798 (6) | 0.0210 (2) | |
C1 | 0.15616 (14) | 0.72901 (11) | 0.34151 (8) | 0.0160 (3) | |
H1A | 0.1178 | 0.7368 | 0.4044 | 0.019* | |
O2 | 0.53283 (11) | 0.55007 (8) | 0.39852 (6) | 0.0188 (2) | |
C2 | 0.35047 (14) | 0.71209 (10) | 0.34504 (8) | 0.0141 (3) | |
H2A | 0.4034 | 0.7906 | 0.3641 | 0.017* | |
O3 | 0.33736 (12) | 0.61674 (8) | 0.48872 (6) | 0.0219 (2) | |
H3 | 0.3807 | 0.5638 | 0.5236 | 0.033* | |
C3 | 0.40618 (14) | 0.68316 (10) | 0.24926 (7) | 0.0135 (3) | |
H3A | 0.4327 | 0.5953 | 0.2465 | 0.016* | |
C4 | 0.25626 (14) | 0.71016 (10) | 0.17863 (8) | 0.0148 (3) | |
H4A | 0.2946 | 0.7028 | 0.1157 | 0.018* | |
C5 | 0.19028 (15) | 0.83791 (10) | 0.19406 (8) | 0.0169 (3) | |
H5A | 0.1055 | 0.8599 | 0.1444 | 0.020* | |
H5B | 0.2849 | 0.8961 | 0.1941 | 0.020* | |
C6 | 0.10856 (15) | 0.84268 (11) | 0.28620 (8) | 0.0181 (3) | |
H6A | 0.1487 | 0.9150 | 0.3204 | 0.022* | |
H6B | −0.0161 | 0.8480 | 0.2758 | 0.022* | |
C7 | 0.06974 (15) | 0.62064 (11) | 0.29348 (8) | 0.0188 (3) | |
H7A | −0.0546 | 0.6272 | 0.2959 | 0.023* | |
H7B | 0.1073 | 0.5453 | 0.3245 | 0.023* | |
C8 | 0.11666 (15) | 0.61758 (11) | 0.19320 (8) | 0.0180 (3) | |
H8A | 0.1567 | 0.5361 | 0.1780 | 0.022* | |
H8B | 0.0153 | 0.6361 | 0.1526 | 0.022* | |
C9 | 0.41562 (14) | 0.61797 (10) | 0.41280 (8) | 0.0147 (3) | |
C10 | 0.56183 (14) | 0.75308 (10) | 0.22505 (8) | 0.0147 (3) | |
C11 | 0.64421 (14) | 0.71562 (11) | 0.14064 (8) | 0.0154 (3) | |
C12 | 0.73488 (15) | 0.80248 (11) | 0.09565 (8) | 0.0191 (3) | |
H12A | 0.7467 | 0.8812 | 0.1204 | 0.023* | |
C13 | 0.80759 (16) | 0.77527 (12) | 0.01549 (9) | 0.0230 (3) | |
H13A | 0.8669 | 0.8356 | −0.0152 | 0.028* | |
C14 | 0.79381 (16) | 0.65959 (13) | −0.02018 (9) | 0.0245 (3) | |
H14A | 0.8438 | 0.6406 | −0.0752 | 0.029* | |
C15 | 0.70687 (16) | 0.57201 (13) | 0.02484 (9) | 0.0246 (3) | |
H15A | 0.6996 | 0.4926 | 0.0011 | 0.030* | |
C16 | 0.63028 (15) | 0.59953 (11) | 0.10437 (8) | 0.0196 (3) | |
H16A | 0.5686 | 0.5396 | 0.1340 | 0.024* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0203 (4) | 0.0220 (5) | 0.0208 (4) | −0.0053 (3) | 0.0021 (3) | −0.0048 (3) |
C1 | 0.0145 (6) | 0.0178 (6) | 0.0162 (6) | 0.0030 (4) | 0.0036 (4) | 0.0026 (4) |
O2 | 0.0193 (4) | 0.0220 (4) | 0.0154 (4) | 0.0064 (3) | 0.0022 (3) | 0.0017 (3) |
C2 | 0.0148 (6) | 0.0136 (5) | 0.0141 (6) | 0.0005 (4) | 0.0015 (4) | −0.0004 (4) |
O3 | 0.0241 (5) | 0.0278 (5) | 0.0141 (4) | 0.0107 (4) | 0.0039 (3) | 0.0053 (3) |
C3 | 0.0135 (5) | 0.0135 (5) | 0.0136 (5) | 0.0009 (4) | 0.0013 (4) | −0.0002 (4) |
C4 | 0.0132 (5) | 0.0168 (6) | 0.0144 (5) | −0.0004 (4) | −0.0001 (4) | 0.0002 (4) |
C5 | 0.0161 (6) | 0.0164 (6) | 0.0181 (6) | 0.0010 (4) | 0.0005 (5) | 0.0035 (4) |
C6 | 0.0179 (6) | 0.0166 (6) | 0.0198 (6) | 0.0044 (4) | 0.0021 (5) | 0.0012 (5) |
C7 | 0.0147 (6) | 0.0188 (6) | 0.0230 (6) | −0.0016 (4) | 0.0017 (5) | 0.0052 (5) |
C8 | 0.0150 (6) | 0.0175 (6) | 0.0214 (6) | −0.0018 (4) | −0.0003 (5) | −0.0014 (5) |
C9 | 0.0146 (5) | 0.0156 (6) | 0.0137 (5) | −0.0005 (4) | −0.0007 (4) | −0.0017 (4) |
C10 | 0.0128 (5) | 0.0159 (6) | 0.0150 (6) | 0.0016 (4) | −0.0015 (4) | 0.0015 (4) |
C11 | 0.0106 (5) | 0.0203 (6) | 0.0152 (6) | 0.0016 (4) | −0.0013 (4) | 0.0012 (4) |
C12 | 0.0158 (6) | 0.0195 (6) | 0.0219 (6) | 0.0014 (5) | 0.0012 (5) | 0.0023 (5) |
C13 | 0.0175 (6) | 0.0298 (7) | 0.0220 (6) | 0.0012 (5) | 0.0037 (5) | 0.0069 (5) |
C14 | 0.0179 (6) | 0.0401 (8) | 0.0157 (6) | −0.0002 (5) | 0.0027 (5) | −0.0037 (5) |
C15 | 0.0213 (6) | 0.0291 (7) | 0.0237 (6) | −0.0034 (5) | 0.0032 (5) | −0.0094 (5) |
C16 | 0.0167 (6) | 0.0214 (6) | 0.0209 (6) | −0.0025 (5) | 0.0028 (5) | −0.0020 (5) |
O1—C10 | 1.2199 (15) | C6—H6A | 0.9900 |
C1—C7 | 1.5346 (17) | C6—H6B | 0.9900 |
C1—C6 | 1.5369 (16) | C7—C8 | 1.5503 (17) |
C1—C2 | 1.5469 (15) | C7—H7A | 0.9900 |
C1—H1A | 1.0000 | C7—H7B | 0.9900 |
O2—C9 | 1.2251 (15) | C8—H8A | 0.9900 |
C2—C9 | 1.5132 (16) | C8—H8B | 0.9900 |
C2—C3 | 1.5426 (15) | C10—C11 | 1.5033 (16) |
C2—H2A | 1.0000 | C11—C12 | 1.3971 (17) |
O3—C9 | 1.3164 (14) | C11—C16 | 1.3982 (17) |
O3—H3 | 0.8400 | C12—C13 | 1.3835 (18) |
C3—C10 | 1.5195 (15) | C12—H12A | 0.9500 |
C3—C4 | 1.5547 (15) | C13—C14 | 1.391 (2) |
C3—H3A | 1.0000 | C13—H13A | 0.9500 |
C4—C5 | 1.5349 (16) | C14—C15 | 1.387 (2) |
C4—C8 | 1.5356 (16) | C14—H14A | 0.9500 |
C4—H4A | 1.0000 | C15—C16 | 1.3910 (17) |
C5—C6 | 1.5456 (16) | C15—H15A | 0.9500 |
C5—H5A | 0.9900 | C16—H16A | 0.9500 |
C5—H5B | 0.9900 | ||
C7—C1—C6 | 108.31 (10) | C1—C7—C8 | 109.27 (9) |
C7—C1—C2 | 109.35 (9) | C1—C7—H7A | 109.8 |
C6—C1—C2 | 108.98 (9) | C8—C7—H7A | 109.8 |
C7—C1—H1A | 110.1 | C1—C7—H7B | 109.8 |
C6—C1—H1A | 110.1 | C8—C7—H7B | 109.8 |
C2—C1—H1A | 110.1 | H7A—C7—H7B | 108.3 |
C9—C2—C3 | 110.83 (9) | C4—C8—C7 | 109.89 (9) |
C9—C2—C1 | 113.57 (9) | C4—C8—H8A | 109.7 |
C3—C2—C1 | 109.86 (9) | C7—C8—H8A | 109.7 |
C9—C2—H2A | 107.4 | C4—C8—H8B | 109.7 |
C3—C2—H2A | 107.4 | C7—C8—H8B | 109.7 |
C1—C2—H2A | 107.4 | H8A—C8—H8B | 108.2 |
C9—O3—H3 | 109.5 | O2—C9—O3 | 123.05 (10) |
C10—C3—C2 | 113.29 (9) | O2—C9—C2 | 122.70 (10) |
C10—C3—C4 | 109.75 (9) | O3—C9—C2 | 114.24 (9) |
C2—C3—C4 | 108.75 (9) | O1—C10—C11 | 120.15 (10) |
C10—C3—H3A | 108.3 | O1—C10—C3 | 122.48 (10) |
C2—C3—H3A | 108.3 | C11—C10—C3 | 117.21 (10) |
C4—C3—H3A | 108.3 | C12—C11—C16 | 119.04 (11) |
C5—C4—C8 | 110.09 (9) | C12—C11—C10 | 117.90 (11) |
C5—C4—C3 | 109.33 (9) | C16—C11—C10 | 123.04 (11) |
C8—C4—C3 | 107.50 (9) | C13—C12—C11 | 120.80 (12) |
C5—C4—H4A | 110.0 | C13—C12—H12A | 119.6 |
C8—C4—H4A | 110.0 | C11—C12—H12A | 119.6 |
C3—C4—H4A | 110.0 | C12—C13—C14 | 119.95 (12) |
C4—C5—C6 | 109.22 (9) | C12—C13—H13A | 120.0 |
C4—C5—H5A | 109.8 | C14—C13—H13A | 120.0 |
C6—C5—H5A | 109.8 | C15—C14—C13 | 119.74 (12) |
C4—C5—H5B | 109.8 | C15—C14—H14A | 120.1 |
C6—C5—H5B | 109.8 | C13—C14—H14A | 120.1 |
H5A—C5—H5B | 108.3 | C14—C15—C16 | 120.56 (12) |
C1—C6—C5 | 109.68 (9) | C14—C15—H15A | 119.7 |
C1—C6—H6A | 109.7 | C16—C15—H15A | 119.7 |
C5—C6—H6A | 109.7 | C15—C16—C11 | 119.88 (12) |
C1—C6—H6B | 109.7 | C15—C16—H16A | 120.1 |
C5—C6—H6B | 109.7 | C11—C16—H16A | 120.1 |
H6A—C6—H6B | 108.2 | ||
C7—C1—C2—C9 | −73.31 (12) | C1—C7—C8—C4 | 9.37 (13) |
C6—C1—C2—C9 | 168.48 (9) | C3—C2—C9—O2 | 18.76 (15) |
C7—C1—C2—C3 | 51.44 (12) | C1—C2—C9—O2 | 142.99 (11) |
C6—C1—C2—C3 | −66.77 (12) | C3—C2—C9—O3 | −162.26 (10) |
C9—C2—C3—C10 | −98.22 (11) | C1—C2—C9—O3 | −38.03 (13) |
C1—C2—C3—C10 | 135.46 (10) | C2—C3—C10—O1 | −15.16 (15) |
C9—C2—C3—C4 | 139.46 (9) | C4—C3—C10—O1 | 106.60 (12) |
C1—C2—C3—C4 | 13.14 (12) | C2—C3—C10—C11 | 169.41 (9) |
C10—C3—C4—C5 | −72.95 (11) | C4—C3—C10—C11 | −68.83 (12) |
C2—C3—C4—C5 | 51.49 (12) | O1—C10—C11—C12 | −22.30 (16) |
C10—C3—C4—C8 | 167.56 (9) | C3—C10—C11—C12 | 153.24 (10) |
C2—C3—C4—C8 | −68.00 (11) | O1—C10—C11—C16 | 159.41 (12) |
C8—C4—C5—C6 | 50.74 (12) | C3—C10—C11—C16 | −25.06 (16) |
C3—C4—C5—C6 | −67.14 (11) | C16—C11—C12—C13 | 1.15 (18) |
C7—C1—C6—C5 | −67.71 (12) | C10—C11—C12—C13 | −177.22 (11) |
C2—C1—C6—C5 | 51.15 (12) | C11—C12—C13—C14 | −1.35 (19) |
C4—C5—C6—C1 | 13.14 (13) | C12—C13—C14—C15 | 0.09 (19) |
C6—C1—C7—C8 | 54.02 (12) | C13—C14—C15—C16 | 1.4 (2) |
C2—C1—C7—C8 | −64.62 (12) | C14—C15—C16—C11 | −1.54 (19) |
C5—C4—C8—C7 | −64.17 (12) | C12—C11—C16—C15 | 0.29 (18) |
C3—C4—C8—C7 | 54.83 (12) | C10—C11—C16—C15 | 178.57 (11) |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O2i | 0.84 | 1.81 | 2.6513 (12) | 178 |
Symmetry code: (i) −x+1, −y+1, −z+1. |
Experimental details
Crystal data | |
Chemical formula | C16H18O3 |
Mr | 258.30 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 100 |
a, b, c (Å) | 7.9155 (7), 11.1129 (9), 14.7559 (12) |
β (°) | 93.882 (3) |
V (Å3) | 1295.01 (19) |
Z | 4 |
Radiation type | Cu Kα |
µ (mm−1) | 0.73 |
Crystal size (mm) | 0.49 × 0.30 × 0.17 |
Data collection | |
Diffractometer | Bruker SMART CCD APEXII area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2001) |
Tmin, Tmax | 0.716, 0.886 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7983, 2405, 2350 |
Rint | 0.029 |
(sin θ/λ)max (Å−1) | 0.609 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.038, 0.100, 1.03 |
No. of reflections | 2405 |
No. of parameters | 174 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.33, −0.20 |
Computer programs: APEX2 (Bruker, 2006), SAINT (Bruker, 2005), SHELXTL (Sheldrick, 2008).
O2—C9 | 1.2251 (15) | O3—C9 | 1.3164 (14) |
O2—C9—C2 | 122.70 (10) | O3—C9—C2 | 114.24 (9) |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O2i | 0.84 | 1.81 | 2.6513 (12) | 178 |
Symmetry code: (i) −x+1, −y+1, −z+1. |
Acknowledgements
HWT is grateful to Professor Gree Loober Spoog for helpful consultations. The authors acknowledge support by NSF–CRIF grant No. 0443538.
References
Blackstock, S. C., Lorand, J. P. & Kochi, J. K. (1987). J. Org. Chem. 52, 1451–1460. CSD CrossRef CAS Web of Science Google Scholar
Bruker (2005). SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2006). APEX2. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Deutsch, E. (1972). J. Org. Chem. 37, 3481–3486. CSD CrossRef CAS Web of Science Google Scholar
Scribner, J. D. & Miller, J. A. (1965). J. Chem. Soc. pp. 5377–5380. CrossRef Web of Science Google Scholar
Sheldrick, G. M. (2001). SADABS. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Zimmerman, H. E., King, R. K. & Meinhardt, M. B. (1992). J. Org. Chem. 57, 5484–5492. CSD CrossRef CAS Web of Science Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
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.