Acta Cryst. (2007). E63, o3640 [ doi:10.1107/S1600536807035246 ]
![[epsilon]](/logos/entities/epsiv_rmgif.gif)
-keto acidThe title compound, C9H8O3, adopts a conformation in which both substituents lie nearly coplanar with the ring. Asymmetric units aggregate by centrosymmetric carboxyl pairing. Close offset stacking of rings in parallel planes creates intermolecular C
C ![[pi]](/logos/entities/pi_rmgif.gif)
- contacts of 3.322 (3) and 3.352 (3) Å, with an accompanying CO - contact of 3.147 (3) Å and similarly close interactions between O atoms and aromatic systems. One close intermolecular C-HO contact is also present.
The title compound was purchased from Acros Organics/Fisher Scientific, Springfield, NJ, USA, and recrystallized from acetic acid, mp 483 K. Typically for carboxyl-paired keto acids, the solid-state (KBr) infrared spectrum features a broad asymmetric absorption at 1683 cm-1 for both C=O functions; in CHCl3 solution this peak is seen at 1689 cm-1.
All H atoms 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 methyl H atoms were put in ideally staggered positions with C—H distances of 0.98 Å and Uiso(H) = 1.5Ueq(C). The aromatic C—Hs were placed in geometrically idealized positions and constrained to ride on their parent C atoms with C—H distances of 0.95 Å and Uiso(H) = 1.2Ueq(C).
Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2004); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.
![[Figure 1]](./lh2466fig1thm.gif)
| Fig. 1. The asymmetric unit with displacement ellipsoids shown at the 30% probability level. |
![[Figure 2]](./lh2466fig2thm.gif)
| Fig. 2. A partial packing diagram, showing the centrosymmetric dimerization of the asymmetric unit. For clarity all carbon-bound H atoms have been removed. Displacement ellipsoids are shown at the 30% probability level. |
| C9H8O3 | F(000) = 344 |
| Mr = 164.15 | Dx = 1.462 Mg m−3 |
| Monoclinic, P21/c | Melting point: 483 K |
| Hall symbol: -P 2ybc | Cu Kα radiation, λ = 1.54178 Å |
| a = 5.3887 (3) Å | Cell parameters from 3385 reflections |
| b = 4.9490 (3) Å | θ = 3.2–68.0° |
| c = 28.1011 (16) Å | µ = 0.93 mm−1 |
| β = 95.478 (4)° | T = 100 K |
| V = 746.00 (7) Å3 | Thin platelet, colourless |
| Z = 4 | 0.35 × 0.18 × 0.05 mm |
| Bruker SMART CCD APEXII area-detector diffractometer | 1226 independent reflections |
| Radiation source: fine-focus sealed tube | 992 reflections with I > 2σ(I) |
| graphite | Rint = 0.029 |
| φ and ω scans | θmax = 68.0°, θmin = 3.2° |
| Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | h = −5→6 |
| Tmin = 0.738, Tmax = 0.957 | k = −5→5 |
| 3378 measured reflections | l = −32→33 |
| Refinement on F2 | Primary atom site location: structure-invariant direct methods |
| Least-squares matrix: full | Secondary atom site location: difference Fourier map |
| R[F2 > 2σ(F2)] = 0.051 | Hydrogen site location: inferred from neighbouring sites |
| wR(F2) = 0.156 | H-atom parameters constrained |
| S = 1.12 | w = 1/[σ2(Fo2) + (0.0946P)2 + 0.1889P] where P = (Fo2 + 2Fc2)/3 |
| 1226 reflections | (Δ/σ)max < 0.001 |
| 111 parameters | Δρmax = 0.27 e Å−3 |
| 0 restraints | Δρmin = −0.29 e Å−3 |
| C9H8O3 | V = 746.00 (7) Å3 |
| Mr = 164.15 | Z = 4 |
| Monoclinic, P21/c | Cu Kα radiation |
| a = 5.3887 (3) Å | µ = 0.93 mm−1 |
| b = 4.9490 (3) Å | T = 100 K |
| c = 28.1011 (16) Å | 0.35 × 0.18 × 0.05 mm |
| β = 95.478 (4)° |
| Bruker SMART CCD APEXII area-detector diffractometer | 1226 independent reflections |
| Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | 992 reflections with I > 2σ(I) |
| Tmin = 0.738, Tmax = 0.957 | Rint = 0.029 |
| 3378 measured reflections | θmax = 68.0° |
| R[F2 > 2σ(F2)] = 0.051 | H-atom parameters constrained |
| wR(F2) = 0.156 | Δρmax = 0.27 e Å−3 |
| S = 1.12 | Δρmin = −0.29 e Å−3 |
| 1226 reflections | Absolute structure: ? |
| 111 parameters | Flack parameter: ? |
| 0 restraints | Rogers parameter: ? |
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 | 0.3411 (4) | 0.9939 (4) | 0.41921 (8) | 0.0224 (5) | |
| O1 | −0.0882 (3) | 1.7124 (3) | 0.31732 (6) | 0.0304 (5) | |
| C2 | 0.4809 (4) | 1.0345 (4) | 0.38039 (8) | 0.0234 (5) | |
| H2 | 0.6238 | 0.9265 | 0.3769 | 0.028* | |
| O2 | 0.2903 (3) | 0.7448 (3) | 0.48987 (5) | 0.0261 (4) | |
| C3 | 0.4105 (4) | 1.2319 (4) | 0.34710 (8) | 0.0238 (5) | |
| H3 | 0.5077 | 1.2615 | 0.3211 | 0.029* | |
| O3 | 0.6124 (3) | 0.6451 (3) | 0.44821 (6) | 0.0271 (4) | |
| H3A | 0.6426 | 0.5338 | 0.4706 | 0.041* | |
| C4 | 0.1981 (4) | 1.3887 (4) | 0.35118 (8) | 0.0223 (5) | |
| C5 | 0.0586 (4) | 1.3456 (4) | 0.39016 (8) | 0.0237 (5) | |
| H5 | −0.0861 | 1.4512 | 0.3933 | 0.028* | |
| C6 | 0.1298 (4) | 1.1511 (4) | 0.42392 (8) | 0.0239 (5) | |
| H6 | 0.0351 | 1.1242 | 0.4504 | 0.029* | |
| C7 | 0.4130 (4) | 0.7837 (4) | 0.45532 (8) | 0.0220 (5) | |
| C8 | 0.1112 (4) | 1.6002 (4) | 0.31530 (8) | 0.0235 (5) | |
| C9 | 0.2724 (4) | 1.6640 (5) | 0.27578 (8) | 0.0261 (5) | |
| H9A | 0.2179 | 1.8349 | 0.2605 | 0.039* | |
| H9B | 0.2575 | 1.5187 | 0.2520 | 0.039* | |
| H9C | 0.4466 | 1.6801 | 0.2891 | 0.039* |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| C1 | 0.0226 (11) | 0.0189 (11) | 0.0252 (12) | −0.0021 (8) | 0.0004 (8) | −0.0039 (9) |
| O1 | 0.0247 (9) | 0.0333 (9) | 0.0333 (10) | 0.0056 (7) | 0.0035 (6) | 0.0043 (7) |
| C2 | 0.0202 (11) | 0.0216 (11) | 0.0282 (12) | 0.0001 (8) | 0.0019 (8) | −0.0036 (9) |
| O2 | 0.0267 (9) | 0.0258 (9) | 0.0262 (8) | 0.0028 (6) | 0.0054 (6) | 0.0013 (6) |
| C3 | 0.0218 (12) | 0.0242 (12) | 0.0259 (11) | −0.0024 (8) | 0.0050 (8) | −0.0028 (9) |
| O3 | 0.0262 (9) | 0.0266 (9) | 0.0291 (9) | 0.0070 (6) | 0.0046 (6) | 0.0038 (6) |
| C4 | 0.0217 (11) | 0.0202 (11) | 0.0246 (11) | −0.0025 (8) | −0.0002 (8) | −0.0030 (8) |
| C5 | 0.0187 (11) | 0.0231 (12) | 0.0291 (12) | 0.0003 (8) | 0.0020 (8) | −0.0020 (9) |
| C6 | 0.0233 (11) | 0.0242 (11) | 0.0248 (12) | −0.0007 (8) | 0.0049 (9) | −0.0020 (8) |
| C7 | 0.0205 (11) | 0.0183 (10) | 0.0270 (11) | −0.0018 (8) | 0.0008 (8) | −0.0050 (8) |
| C8 | 0.0222 (11) | 0.0213 (11) | 0.0266 (11) | −0.0013 (8) | −0.0004 (8) | −0.0048 (9) |
| C9 | 0.0257 (12) | 0.0261 (12) | 0.0262 (12) | 0.0015 (8) | 0.0012 (9) | 0.0035 (9) |
| C1—C6 | 1.395 (3) | O3—H3A | 0.8400 |
| C1—C2 | 1.398 (3) | C4—C5 | 1.402 (3) |
| C1—C7 | 1.479 (3) | C4—C8 | 1.497 (3) |
| O1—C8 | 1.216 (3) | C5—C6 | 1.380 (3) |
| C2—C3 | 1.381 (3) | C5—H5 | 0.9500 |
| C2—H2 | 0.9500 | C6—H6 | 0.9500 |
| O2—C7 | 1.241 (3) | C8—C9 | 1.507 (3) |
| C3—C4 | 1.396 (3) | C9—H9A | 0.9800 |
| C3—H3 | 0.9500 | C9—H9B | 0.9800 |
| O3—C7 | 1.306 (2) | C9—H9C | 0.9800 |
| C6—C1—C2 | 119.9 (2) | C5—C6—C1 | 119.98 (19) |
| C6—C1—C7 | 119.33 (18) | C5—C6—H6 | 120.0 |
| C2—C1—C7 | 120.73 (19) | C1—C6—H6 | 120.0 |
| C3—C2—C1 | 119.8 (2) | O2—C7—O3 | 123.1 (2) |
| C3—C2—H2 | 120.1 | O2—C7—C1 | 121.46 (19) |
| C1—C2—H2 | 120.1 | O3—C7—C1 | 115.46 (17) |
| C2—C3—C4 | 120.79 (19) | O1—C8—C4 | 120.59 (19) |
| C2—C3—H3 | 119.6 | O1—C8—C9 | 120.8 (2) |
| C4—C3—H3 | 119.6 | C4—C8—C9 | 118.56 (19) |
| C7—O3—H3A | 109.5 | C8—C9—H9A | 109.5 |
| C3—C4—C5 | 119.0 (2) | C8—C9—H9B | 109.5 |
| C3—C4—C8 | 122.62 (19) | H9A—C9—H9B | 109.5 |
| C5—C4—C8 | 118.41 (19) | C8—C9—H9C | 109.5 |
| C6—C5—C4 | 120.5 (2) | H9A—C9—H9C | 109.5 |
| C6—C5—H5 | 119.7 | H9B—C9—H9C | 109.5 |
| C4—C5—H5 | 119.7 | ||
| C6—C1—C2—C3 | 0.6 (3) | C7—C1—C6—C5 | −179.16 (19) |
| C7—C1—C2—C3 | −179.96 (19) | C6—C1—C7—O2 | −0.3 (3) |
| C1—C2—C3—C4 | −1.3 (3) | C2—C1—C7—O2 | −179.8 (2) |
| C2—C3—C4—C5 | 1.0 (3) | C6—C1—C7—O3 | 179.80 (19) |
| C2—C3—C4—C8 | −178.4 (2) | C2—C1—C7—O3 | 0.4 (3) |
| C3—C4—C5—C6 | −0.1 (3) | C3—C4—C8—O1 | 172.2 (2) |
| C8—C4—C5—C6 | 179.4 (2) | C5—C4—C8—O1 | −7.3 (3) |
| C4—C5—C6—C1 | −0.5 (3) | C3—C4—C8—C9 | −5.8 (3) |
| C2—C1—C6—C5 | 0.3 (3) | C5—C4—C8—C9 | 174.73 (19) |
| D—H···A | D—H | H···A | D···A | D—H···A |
| O3—H3A···O2i | 0.84 | 1.79 | 2.618 (2) | 170 |
| C5—H5···O3ii | 0.95 | 2.53 | 3.375 (2) | 148 |
| Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x−1, y+1, z. |
| D—H···A | D—H | H···A | D···A | D—H···A |
| O3—H3A···O2i | 0.84 | 1.79 | 2.618 (2) | 170 |
| C5—H5···O3ii | 0.95 | 2.53 | 3.375 (2) | 148 |
| Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x−1, y+1, z. |
HWT is grateful to Professor Gree Loober Spoog for helpful consultations. The authors acknowledge support by NSF–CRIF grant No. 0443538.
Borthwick, P. W. (1980). Acta Cryst. B36, 628–632.
Bruker (2005). SAINT (Version 7.23a) and SADABS (Version 2004/1). Bruker AXS Inc., Madison, Wisconsin, USA.
Bruker (2006). APEX2. Version 2.0-2. Bruker AXS Inc., Madison, Wisconsin, USA.
Sheldrick, G. M. (2001). SADABS. Version 2. University of Göttingen, Germany.
Sheldrick, G. M. (2004). SHELXTL. Version 6.14. Bruker AXS Inc., Madison, Wisconsin, USA.
Steiner, T. (1997). J. Chem. Soc. Chem. Commun. pp. 727–734.
Our study of solid-state H-bonding patterns in ketocarboxylic acids has employed several examples of fundamentally simple systems to explore the minimum requirements for various H-bonding modes. Among such compounds is the title aromatic.
Fig. 1 shows the asymmetric unit. Although rotations are formally possible about three of its C—C bonds, the two most consequential are suppressed by conjugative coplanarity requirements, while methyl rotation should have only very slight effects on the packing. Full conjugation requires both carbonyl groups to lie very close to the ring plane, with the acetyl group (O1, C8, C4, C9) and the carboxyl (O2, O3, C7, C1) defining planes whose dihedral angles are respectively 6.75 (16) and 0.46 (16)° relative to the plane of the ring carbons and generating a ketone-versus-carboxyl dihedral angle of 7.03 (18)°. Although the tiitle compound is inherently achiral, this creates a conformational chirality to which the rotational conformation of the methyl contributes further; for the methyl H nearest the ring plane, the torsion angle H9A—C9···C5—H5 = 14.8°.
The C—O bond lengths and C—C—O angles conform to values typical for highly ordered dimeric carboxyls (Borthwick, 1980) and no significant averaging by disorder is observed [O2—C7 = 1.241 (3) & O3—C7 = 1.306 (2) Å; O2—C7—C1 = 121.46 (19) & O3—C7—C1 = 115.46 (17)°].
Fig. 2 illustrates the packing of the chosen cell, in which asymmetric units associate as H-bonded centrosymmetric dimers whose two halves lie in planes separated by 0.231 Å. Two sets of these dimers, screw-related and centered at 1/2,1/2,1/2 and at 1/2,0,0, lie in planes whose dihedral angle is 84.79 (5)°. Dimers of each type stack translationally in planes separated by 0.583 (3) & 3.337 (3) Å. The former arrangement involves a molecular offset to the side, without ring overlap but close enough to create several relatively short C—H···O intermolecular approaches (Steiner, 1997). These include one H···O contact of 2.53 Å (between H5 and O3), plus another three that lie narrowly (2.61–2.62 Å) beyond the range normally accepted for these close contacts (2.60 Å). For the larger interplanar separation, the offset is only half a molecule each in both length and width, creating close intermolecular sp2 contacts of 3.147 (3) Å (C7···O2), 3.352 (3) Å (C2···C8) and 3.322 (3) Å (C5···C7). This arrangement does not involve pi-stacking of the rings themselves, but places both O1 and O3 over adjacent aromatic ring-centers at distances of 3.506 (3) & 3.313 (3) Å to the respective centroids. All of these presumably represent attractive pi interactions.