Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807043206/lh2498sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536807043206/lh2498Isup2.hkl |
CCDC reference: 663726
Key indicators
- Single-crystal X-ray study
- T = 100 K
- Mean (C-C) = 0.002 Å
- R factor = 0.037
- wR factor = 0.102
- Data-to-parameter ratio = 13.5
checkCIF/PLATON results
No syntax errors found
Alert level A PLAT027_ALERT_3_A _diffrn_reflns_theta_full (too) Low ............ 64.84 Deg.
Author Response: diffrn reflns theta full (too) Low...64.84\%. (Alert level A) and resolution (too) Low [sin\q/\l < 0.6] (Alert level C): this problem has arisen because initially we were told by the manufacturer of our newly-installed Bruker Smart Apex II unit that we could collect our small-molecule data to only 0.85\%A resolution (with copper K\a radiation). This yields a \q max. of ca. 64.84\%, less than the current 67\% required by Acta. However, since the crystals of this compound are no longer available (or are of such small size as to preclude collecting a new data set), we can only rely on the current data set. |
Alert level C THETM01_ALERT_3_C The value of sine(theta_max)/wavelength is less than 0.590 Calculated sin(theta_max)/wavelength = 0.5871 PLAT023_ALERT_3_C Resolution (too) Low [sin(th)/Lambda < 0.6]..... 64.84 Deg. PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low ....... 0.98 PLAT152_ALERT_1_C Supplied and Calc Volume s.u. Inconsistent ..... ? PLAT720_ALERT_4_C Number of Unusual/Non-Standard Label(s) ........ 2
Alert level G PLAT793_ALERT_1_G Check the Absolute Configuration of C2 = ... R PLAT793_ALERT_1_G Check the Absolute Configuration of C4A = ... R PLAT793_ALERT_1_G Check the Absolute Configuration of C8A = ... R
1 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 5 ALERT level C = Check and explain 3 ALERT level G = General alerts; check 4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 0 ALERT type 2 Indicator that the structure model may be wrong or deficient 4 ALERT type 3 Indicator that the structure quality may be low 1 ALERT type 4 Improvement, methodology, query or suggestion 0 ALERT type 5 Informative message, check
The title compound has not previously been reported. The corresponding Δ4a,5 keto acid, prepared as described by Malak et al. (2007), was hydrogenated over Pd/C in absolute ethanol solution and yielded material mp 405 when recrystallized from Et2O/hexane. The stereochemistry obtained for C2 versus C8a arises prior to the hydrogenation, probably as a result of equilibrations during saponification or earlier (House et al., 1965), while the cis ring-juncture stereochemistry obtained in the reduction is typical of results in a variety of octalones.
The solid-state (KBr) infrared spectrum of (I) has C=O absorptions at 1721 & 1678 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. In CHCl3 solution, where dimers predominate, these bands coalesce and appear at 1706 cm-1.
All H atoms for (I) were found in electron-density difference maps. The O—H was constrained to an idealized position with distance fixed at 0.84 Å and Uiso(H) = 1.5Ueq(O). The methylene and methine Hs were placed in geometrically idealized positions and constrained to ride on their parent C atoms with C—H distances of 0.99 and 1.00 Å, respectively, and Uiso(H) = 1.2Ueq(C).
Among the five H-bonding modes known for ketocarboxylic acids, dimers are found most often. However, we have shown that acid-to-ketone catemers occur more frequently when centrosymmetry is thwarted or disfavored, as well as among conformationally constrained molecules. The latter is the case for the title compound.
Fig. 1 shows the asymmetric unit with its numbering. In principle, the flexibility of the cis-decalin system permits either of two double-chair conformations. However, the disfavored arrangement would place the side-chain on an axial bond on the inside of the system's curvature, resulting in serious steric interference with an axial H at C8. The C2—C9 staggering requires that C10 have a gauche interaction with an equatorial hydrogen either at C1 or C3. Such gauche arrangements are less serious here than in systems where all centers are tetrahedral, because the carboxyl's sp2 hybridization diminishes the steric repulsions involved. The observed C2—C9 conformation has torsion angle C3—C2—C9—C10 = -174.51 (13)°). Within the asymmetric unit, any energy advantage for this arrangement appears so slight that the choice is likely dictated by packing considerations. The remaining available rotation yields a C2—C9—C10—O3 torsion angle of 41.98 (19)° for the carboxyl group.
The averaging of C—O bond lengths and C—C—O angles by disorder often found in carboxyl dimers it is not seen in H-bonding modes whose geometries exclude the averaging mechanisms responsible. Because the title compound's aggregation is not dimeric, these bond lengths and angles are typical of those in highly ordered dimeric carboxyls.
Fig. 2 shows the packing of the cell, with extra molecules included to illustrate the acid-to-ketone H-bonding scheme. Each carboxylic acid is linked to the ketone in a molecule translationally related in the b direction [O···O = 2.6816 (17) Å; O—H···O = 169°], with each of the cell's eight molecules participating in a separate H-bonding chain. These eight parallel chains appear as four counterdirectional pairs arrayed centrosymmetrically about 1/2,1/2,1/2.
We characterize the geometry of H bonding to carbonyls using a combination of the H···O=C angle and the H···O=C—C torsional angle. These describe the approach of the H atom to the O in terms of its deviation from, respectively, C=O axiality (ideal = 120°) and planarity with the carbonyl (ideal = 0°). Here, these angles are 125 & -7.5°.
Three intermolecular close contacts were found within the 2.6 Å range we standardly survey for non-bonded C—H···O packing interactions (Table 1).
For related literature, see: House et al. (1965); Malak et al. (2007).
Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2004); program(s) used to refine structure: SHELXTL (Sheldrick, 2004); molecular graphics: SHELXTL (Sheldrick, 2004); software used to prepare material for publication: SHELXTL (Sheldrick, 2004).
C12H18O3 | F(000) = 912 |
Mr = 210.26 | Dx = 1.253 Mg m−3 |
Monoclinic, C2/c | Melting point: 405 K |
Hall symbol: -C 2yc | Cu Kα radiation, λ = 1.54178 Å |
a = 21.1804 (4) Å | Cell parameters from 11741 reflections |
b = 10.1644 (2) Å | θ = 4.6–64.8° |
c = 11.3208 (3) Å | µ = 0.72 mm−1 |
β = 113.841 (2)° | T = 100 K |
V = 2229.24 (8) Å3 | Parallelepiped, colourless |
Z = 8 | 0.39 × 0.25 × 0.25 mm |
Bruker SMART CCD APEX II area-detector diffractometer | 1848 independent reflections |
Radiation source: fine-focus sealed tube | 1516 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.057 |
φ and ω scans | θmax = 64.8°, θmin = 4.6° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | h = −24→24 |
Tmin = 0.767, Tmax = 0.841 | k = −11→11 |
11737 measured reflections | l = −11→12 |
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)] = 0.037 | H-atom parameters constrained |
wR(F2) = 0.102 | w = 1/[σ2(Fo2) + (0.0533P)2 + 1.3738P] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max < 0.001 |
1848 reflections | Δρmax = 0.31 e Å−3 |
137 parameters | Δρmin = −0.15 e Å−3 |
0 restraints | Extinction correction: SHELXTL (Sheldrick, 2004) |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: none |
C12H18O3 | V = 2229.24 (8) Å3 |
Mr = 210.26 | Z = 8 |
Monoclinic, C2/c | Cu Kα radiation |
a = 21.1804 (4) Å | µ = 0.72 mm−1 |
b = 10.1644 (2) Å | T = 100 K |
c = 11.3208 (3) Å | 0.39 × 0.25 × 0.25 mm |
β = 113.841 (2)° |
Bruker SMART CCD APEX II area-detector diffractometer | 1848 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | 1516 reflections with I > 2σ(I) |
Tmin = 0.767, Tmax = 0.841 | Rint = 0.057 |
11737 measured reflections |
R[F2 > 2σ(F2)] = 0.037 | 0 restraints |
wR(F2) = 0.102 | H-atom parameters constrained |
S = 1.04 | Δρmax = 0.31 e Å−3 |
1848 reflections | Δρmin = −0.15 e Å−3 |
137 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 | ||
C1 | 0.12293 (7) | 0.55256 (15) | 0.08048 (14) | 0.0208 (3) | |
H1A | 0.1606 | 0.6001 | 0.1498 | 0.025* | |
H1B | 0.1081 | 0.4792 | 0.1208 | 0.025* | |
O1 | 0.10016 (6) | 1.02711 (11) | 0.15128 (12) | 0.0359 (3) | |
C2 | 0.15039 (7) | 0.49638 (14) | −0.01477 (14) | 0.0213 (3) | |
H2A | 0.1128 | 0.4436 | −0.0809 | 0.026* | |
O2 | 0.23668 (6) | 0.24042 (12) | 0.21637 (11) | 0.0348 (3) | |
C3 | 0.16989 (8) | 0.60852 (15) | −0.08379 (16) | 0.0260 (4) | |
H3A | 0.2084 | 0.6596 | −0.0201 | 0.031* | |
H3B | 0.1858 | 0.5714 | −0.1479 | 0.031* | |
O3 | 0.13891 (6) | 0.22685 (11) | 0.04077 (11) | 0.0324 (3) | |
H3 | 0.1322 | 0.1624 | 0.0807 | 0.049* | |
C4 | 0.10842 (9) | 0.69988 (16) | −0.15210 (15) | 0.0285 (4) | |
H4A | 0.1232 | 0.7730 | −0.1928 | 0.034* | |
H4B | 0.0718 | 0.6503 | −0.2216 | 0.034* | |
C4A | 0.07856 (8) | 0.75706 (15) | −0.06068 (14) | 0.0237 (4) | |
H4AA | 0.0343 | 0.8022 | −0.1145 | 0.028* | |
C5 | 0.12764 (8) | 0.86090 (16) | 0.02976 (15) | 0.0254 (4) | |
H5A | 0.1742 | 0.8220 | 0.0735 | 0.030* | |
H5B | 0.1313 | 0.9363 | −0.0226 | 0.030* | |
C6 | 0.10384 (8) | 0.90974 (16) | 0.12963 (16) | 0.0262 (4) | |
C7 | 0.08506 (9) | 0.80542 (16) | 0.20388 (16) | 0.0282 (4) | |
H7A | 0.0631 | 0.8470 | 0.2569 | 0.034* | |
H7B | 0.1275 | 0.7601 | 0.2629 | 0.034* | |
C8 | 0.03537 (8) | 0.70459 (16) | 0.11229 (16) | 0.0275 (4) | |
H8A | −0.0098 | 0.7474 | 0.0640 | 0.033* | |
H8B | 0.0281 | 0.6322 | 0.1639 | 0.033* | |
C8A | 0.06196 (7) | 0.64682 (15) | 0.01577 (14) | 0.0222 (3) | |
H8AA | 0.0234 | 0.5938 | −0.0479 | 0.027* | |
C9 | 0.21235 (8) | 0.40612 (16) | 0.05273 (16) | 0.0262 (4) | |
H9A | 0.2308 | 0.3787 | −0.0111 | 0.031* | |
H9B | 0.2489 | 0.4574 | 0.1206 | 0.031* | |
C10 | 0.19796 (7) | 0.28470 (15) | 0.11360 (15) | 0.0229 (3) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0221 (7) | 0.0191 (8) | 0.0203 (7) | −0.0016 (6) | 0.0075 (6) | 0.0014 (6) |
O1 | 0.0488 (7) | 0.0217 (6) | 0.0414 (7) | −0.0043 (5) | 0.0228 (6) | −0.0076 (5) |
C2 | 0.0211 (7) | 0.0202 (8) | 0.0215 (8) | −0.0015 (6) | 0.0072 (6) | −0.0014 (6) |
O2 | 0.0273 (6) | 0.0412 (8) | 0.0292 (7) | 0.0041 (5) | 0.0043 (5) | 0.0073 (5) |
C3 | 0.0324 (8) | 0.0242 (8) | 0.0264 (9) | −0.0012 (7) | 0.0171 (7) | −0.0012 (6) |
O3 | 0.0322 (6) | 0.0251 (6) | 0.0297 (6) | −0.0043 (5) | 0.0020 (5) | 0.0036 (5) |
C4 | 0.0396 (9) | 0.0248 (8) | 0.0230 (8) | 0.0010 (7) | 0.0146 (7) | 0.0030 (6) |
C4A | 0.0261 (8) | 0.0206 (8) | 0.0213 (8) | 0.0018 (6) | 0.0062 (6) | 0.0020 (6) |
C5 | 0.0293 (8) | 0.0212 (8) | 0.0280 (8) | −0.0013 (6) | 0.0139 (6) | 0.0025 (6) |
C6 | 0.0246 (8) | 0.0245 (9) | 0.0265 (8) | −0.0019 (6) | 0.0072 (6) | −0.0033 (6) |
C7 | 0.0337 (8) | 0.0269 (9) | 0.0282 (9) | −0.0008 (7) | 0.0168 (7) | −0.0032 (7) |
C8 | 0.0260 (8) | 0.0249 (9) | 0.0342 (9) | −0.0002 (6) | 0.0148 (7) | 0.0003 (7) |
C8A | 0.0219 (7) | 0.0206 (8) | 0.0228 (8) | −0.0010 (6) | 0.0076 (6) | 0.0001 (6) |
C9 | 0.0208 (7) | 0.0258 (8) | 0.0314 (9) | 0.0023 (6) | 0.0098 (6) | 0.0007 (7) |
C10 | 0.0209 (7) | 0.0229 (8) | 0.0246 (8) | 0.0065 (6) | 0.0090 (6) | −0.0032 (6) |
C1—C2 | 1.528 (2) | C4A—C8A | 1.541 (2) |
C1—C8A | 1.536 (2) | C4A—C5 | 1.544 (2) |
C1—H1A | 0.9900 | C4A—H4AA | 1.0000 |
C1—H1B | 0.9900 | C5—C6 | 1.496 (2) |
O1—C6 | 1.227 (2) | C5—H5A | 0.9900 |
C2—C9 | 1.529 (2) | C5—H5B | 0.9900 |
C2—C3 | 1.530 (2) | C6—C7 | 1.503 (2) |
C2—H2A | 1.0000 | C7—C8 | 1.533 (2) |
O2—C10 | 1.207 (2) | C7—H7A | 0.9900 |
C3—C4 | 1.530 (2) | C7—H7B | 0.9900 |
C3—H3A | 0.9900 | C8—C8A | 1.534 (2) |
C3—H3B | 0.9900 | C8—H8A | 0.9900 |
O3—C10 | 1.3252 (19) | C8—H8B | 0.9900 |
O3—H3 | 0.8400 | C8A—H8AA | 1.0000 |
C4—C4A | 1.529 (2) | C9—C10 | 1.504 (2) |
C4—H4A | 0.9900 | C9—H9A | 0.9900 |
C4—H4B | 0.9900 | C9—H9B | 0.9900 |
C2—C1—C8A | 112.53 (12) | C6—C5—H5B | 109.1 |
C2—C1—H1A | 109.1 | C4A—C5—H5B | 109.1 |
C8A—C1—H1A | 109.1 | H5A—C5—H5B | 107.8 |
C2—C1—H1B | 109.1 | O1—C6—C5 | 122.79 (15) |
C8A—C1—H1B | 109.1 | O1—C6—C7 | 121.45 (15) |
H1A—C1—H1B | 107.8 | C5—C6—C7 | 115.76 (14) |
C1—C2—C9 | 111.49 (12) | C6—C7—C8 | 110.96 (13) |
C1—C2—C3 | 109.89 (12) | C6—C7—H7A | 109.4 |
C9—C2—C3 | 110.36 (12) | C8—C7—H7A | 109.4 |
C1—C2—H2A | 108.3 | C6—C7—H7B | 109.4 |
C9—C2—H2A | 108.3 | C8—C7—H7B | 109.4 |
C3—C2—H2A | 108.3 | H7A—C7—H7B | 108.0 |
C4—C3—C2 | 111.11 (12) | C7—C8—C8A | 112.85 (12) |
C4—C3—H3A | 109.4 | C7—C8—H8A | 109.0 |
C2—C3—H3A | 109.4 | C8A—C8—H8A | 109.0 |
C4—C3—H3B | 109.4 | C7—C8—H8B | 109.0 |
C2—C3—H3B | 109.4 | C8A—C8—H8B | 109.0 |
H3A—C3—H3B | 108.0 | H8A—C8—H8B | 107.8 |
C10—O3—H3 | 109.5 | C8—C8A—C1 | 112.28 (12) |
C4A—C4—C3 | 112.88 (13) | C8—C8A—C4A | 110.76 (13) |
C4A—C4—H4A | 109.0 | C1—C8A—C4A | 112.51 (12) |
C3—C4—H4A | 109.0 | C8—C8A—H8AA | 107.0 |
C4A—C4—H4B | 109.0 | C1—C8A—H8AA | 107.0 |
C3—C4—H4B | 109.0 | C4A—C8A—H8AA | 107.0 |
H4A—C4—H4B | 107.8 | C10—C9—C2 | 115.43 (12) |
C4—C4A—C8A | 110.76 (13) | C10—C9—H9A | 108.4 |
C4—C4A—C5 | 110.91 (13) | C2—C9—H9A | 108.4 |
C8A—C4A—C5 | 111.72 (12) | C10—C9—H9B | 108.4 |
C4—C4A—H4AA | 107.8 | C2—C9—H9B | 108.4 |
C8A—C4A—H4AA | 107.8 | H9A—C9—H9B | 107.5 |
C5—C4A—H4AA | 107.8 | O2—C10—O3 | 122.47 (15) |
C6—C5—C4A | 112.69 (13) | O2—C10—C9 | 124.27 (14) |
C6—C5—H5A | 109.1 | O3—C10—C9 | 113.22 (13) |
C4A—C5—H5A | 109.1 | ||
C8A—C1—C2—C9 | 178.32 (12) | C6—C7—C8—C8A | 52.53 (18) |
C8A—C1—C2—C3 | 55.63 (16) | C7—C8—C8A—C1 | 71.69 (17) |
C1—C2—C3—C4 | −56.71 (16) | C7—C8—C8A—C4A | −55.02 (17) |
C9—C2—C3—C4 | 179.93 (13) | C2—C1—C8A—C8 | −179.09 (12) |
C2—C3—C4—C4A | 56.59 (17) | C2—C1—C8A—C4A | −53.33 (16) |
C3—C4—C4A—C8A | −52.68 (17) | C4—C4A—C8A—C8 | 177.19 (12) |
C3—C4—C4A—C5 | 71.97 (17) | C5—C4A—C8A—C8 | 53.01 (16) |
C4—C4A—C5—C6 | −174.28 (13) | C4—C4A—C8A—C1 | 50.61 (16) |
C8A—C4A—C5—C6 | −50.18 (17) | C5—C4A—C8A—C1 | −73.58 (16) |
C4A—C5—C6—O1 | −130.97 (16) | C1—C2—C9—C10 | 63.15 (17) |
C4A—C5—C6—C7 | 49.60 (19) | C3—C2—C9—C10 | −174.43 (13) |
O1—C6—C7—C8 | 130.45 (16) | C2—C9—C10—O2 | −140.42 (16) |
C5—C6—C7—C8 | −50.12 (18) | C2—C9—C10—O3 | 41.91 (19) |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O1i | 0.84 | 1.85 | 2.6816 (17) | 169 |
C1—H1A···O2ii | 0.99 | 2.53 | 3.4997 (18) | 167 |
C5—H5A···O2ii | 0.99 | 2.51 | 3.368 (2) | 145 |
C8—H8A···O3iii | 0.99 | 2.52 | 3.4559 (19) | 158 |
Symmetry codes: (i) x, y−1, z; (ii) −x+1/2, y+1/2, −z+1/2; (iii) −x, −y+1, −z. |
Experimental details
Crystal data | |
Chemical formula | C12H18O3 |
Mr | 210.26 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 100 |
a, b, c (Å) | 21.1804 (4), 10.1644 (2), 11.3208 (3) |
β (°) | 113.841 (2) |
V (Å3) | 2229.24 (8) |
Z | 8 |
Radiation type | Cu Kα |
µ (mm−1) | 0.72 |
Crystal size (mm) | 0.39 × 0.25 × 0.25 |
Data collection | |
Diffractometer | Bruker SMART CCD APEX II area-detector |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2001) |
Tmin, Tmax | 0.767, 0.841 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 11737, 1848, 1516 |
Rint | 0.057 |
(sin θ/λ)max (Å−1) | 0.587 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.037, 0.102, 1.04 |
No. of reflections | 1848 |
No. of parameters | 137 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.31, −0.15 |
Computer programs: APEX2 (Bruker, 2006), SAINT (Bruker, 2005), SHELXTL (Sheldrick, 2004).
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O1i | 0.84 | 1.85 | 2.6816 (17) | 169 |
C1—H1A···O2ii | 0.99 | 2.53 | 3.4997 (18) | 167 |
C5—H5A···O2ii | 0.99 | 2.51 | 3.368 (2) | 145 |
C8—H8A···O3iii | 0.99 | 2.52 | 3.4559 (19) | 158 |
Symmetry codes: (i) x, y−1, z; (ii) −x+1/2, y+1/2, −z+1/2; (iii) −x, −y+1, −z. |
Among the five H-bonding modes known for ketocarboxylic acids, dimers are found most often. However, we have shown that acid-to-ketone catemers occur more frequently when centrosymmetry is thwarted or disfavored, as well as among conformationally constrained molecules. The latter is the case for the title compound.
Fig. 1 shows the asymmetric unit with its numbering. In principle, the flexibility of the cis-decalin system permits either of two double-chair conformations. However, the disfavored arrangement would place the side-chain on an axial bond on the inside of the system's curvature, resulting in serious steric interference with an axial H at C8. The C2—C9 staggering requires that C10 have a gauche interaction with an equatorial hydrogen either at C1 or C3. Such gauche arrangements are less serious here than in systems where all centers are tetrahedral, because the carboxyl's sp2 hybridization diminishes the steric repulsions involved. The observed C2—C9 conformation has torsion angle C3—C2—C9—C10 = -174.51 (13)°). Within the asymmetric unit, any energy advantage for this arrangement appears so slight that the choice is likely dictated by packing considerations. The remaining available rotation yields a C2—C9—C10—O3 torsion angle of 41.98 (19)° for the carboxyl group.
The averaging of C—O bond lengths and C—C—O angles by disorder often found in carboxyl dimers it is not seen in H-bonding modes whose geometries exclude the averaging mechanisms responsible. Because the title compound's aggregation is not dimeric, these bond lengths and angles are typical of those in highly ordered dimeric carboxyls.
Fig. 2 shows the packing of the cell, with extra molecules included to illustrate the acid-to-ketone H-bonding scheme. Each carboxylic acid is linked to the ketone in a molecule translationally related in the b direction [O···O = 2.6816 (17) Å; O—H···O = 169°], with each of the cell's eight molecules participating in a separate H-bonding chain. These eight parallel chains appear as four counterdirectional pairs arrayed centrosymmetrically about 1/2,1/2,1/2.
We characterize the geometry of H bonding to carbonyls using a combination of the H···O=C angle and the H···O=C—C torsional angle. These describe the approach of the H atom to the O in terms of its deviation from, respectively, C=O axiality (ideal = 120°) and planarity with the carbonyl (ideal = 0°). Here, these angles are 125 & -7.5°.
Three intermolecular close contacts were found within the 2.6 Å range we standardly survey for non-bonded C—H···O packing interactions (Table 1).