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Acta Crystallogr Sect E Struct Rep Online. 2010 July 1; 66(Pt 7): o1595.
Published online 2010 June 5. doi:  10.1107/S1600536810021094
PMCID: PMC3006848

3-Acetyl­benzoic acid


In the crystal structure of the title compound, C9H8O3, essentially planar mol­ecules [the carboxyl group makes a dihedral angle of 4.53 (7)° with the plane of the ring, while the acid group forms a dihedral angle of 3.45 (8)° to the ring] aggregate by centrosymmetric hydrogen-bond pairing of ordered carboxyl groups. This yields dimers which have two orientations in a unit cell, creating a herringbone pattern. In addition, two close C—H(...)O inter­molecular contacts exist: one is between a methyl H atom and the ketone of a symmetry-related mol­ecule and the other involves a benzene H atom and the carboxyl group O atom of another mol­ecule. The crystal studied was a non-merohedral twin with twin law [100, 0An external file that holds a picture, illustration, etc.
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Object name is e-66-o1595-efi1.jpg0An external file that holds a picture, illustration, etc.
Object name is e-66-o1595-efi1.jpg] and a domain ratio of 0.8104(14): 0.1896(14).

Related literature

For a discussion of highly ordered carboxyl bond distances and angles, see: Borthwick (1980 [triangle]). For the use of the twin law, see: Cooper et al. (2002 [triangle]). For the structure of the ortho-isomer, see: Dobson & Gerkin (1996 [triangle]). For the structure of the para-isomer, see: Lalancette et al. (2007 [triangle]).

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Object name is e-66-o1595-scheme1.jpg


Crystal data

  • C9H8O3
  • M r = 164.15
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-66-o1595-efi4.jpg
  • a = 3.8202 (1) Å
  • b = 15.6478 (3) Å
  • c = 12.9282 (3) Å
  • β = 98.508 (1)°
  • V = 764.31 (3) Å3
  • Z = 4
  • Cu Kα radiation
  • μ = 0.90 mm−1
  • T = 100 K
  • 0.20 × 0.18 × 0.11 mm

Data collection

  • Bruker SMART CCD APEXII area-detector diffractometer
  • Absorption correction: numerical (SADABS; Sheldrick, 2008a [triangle]) T min = 0.840, T max = 0.907
  • 7201 measured reflections
  • 1386 independent reflections
  • 1351 reflections with I > 2σ(I)
  • R int = 0.023


  • R[F 2 > 2σ(F 2)] = 0.031
  • wR(F 2) = 0.085
  • S = 1.06
  • 1386 reflections
  • 115 parameters
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 0.18 e Å−3
  • Δρmin = −0.20 e Å−3

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

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810021094/lh5054sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810021094/lh5054Isup2.hkl

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


The authors acknowledge support by NSF–CRIF grant No. 0443538. This paper is dedicated to the memory of HWT; he was a wonderful mentor, teacher and friend at Rutgers University-Newark for over 44 years.

supplementary crystallographic information


Since keto carboxylic acids can crystallize in five different hydrogen-bonding modes, these types of compounds always present a challenge to predict a priori what the H-bonding mode will be. Three of these modes are either relatively rare or have geometries which preclude some structures. Racemates crystallize with a center of symmetry and generally produce an H-bonded dimer between the acid groups.

Fig. 1 presents a view of the asymmetric unit of the title compound (I) with its numbering scheme. The conjugation in this δ-keto acid requires that both the acid and ketone groups are close to the ring plane; the carboxyl (C3—C8—C9—O1) makes a dihedral angle of 4.53 (7)° with the plane of the ring, while the acid (C1—C7—O2—O3) forms a dihedral angle of 3.45 (8)° to the ring (in the same direction). The molecule adopts a chiral conformation by the flexing of both the methyl group and the hydroxyl group away from the plane of the rest of the atoms in the same direction; this induced chirality is due to the packing of the molecules. This flexing then generates a total dihedral angle between the carboxyl and the acetyl groups of 6.19 (8)°.

Complete or partial averaging of C—O bond lengths and C—C—O angles due to disorder in carboxyl dimers was not found in (I), where these lengths and angles (Table 1) are similar to those in other highly ordered carboxyl situations (Borthwick, 1980).

This meta-acetylbenzoic acid has centrosymmetric H-bonded dimer pairs across two different cell edges in the chosen cell, at (0,0,1/2) & at (0,1/2,0). The parallel planes making up the dimer pair are offset from each other by 0.36 Å. Two sets of these dimers are screw-related and form a herringbone angle of 46.15 (3)° between them in the chosen cell (see Fig 2). Two close C—H···O intermolecular contacts exist: one is between a methyl H atom and the ketone of the adjacent molecule, and the 2nd one is from a phenyl H atom to the carboxyl O atom of another molecule.

Compound (I) crystallizes as a centrosymmetric dimer, just as its isomer 4-acetylbenzoic acid (Lalancette et al., 2007). Unlike both the 3-acetyl and the 4-acetylbenzoic acids, 2-acetylbenzoic acid crystallizes in the phthalide form with a single H-bond betwen the hydroxyl of one molecule and the ketone of the adjacent molecule (Dobson & Gerkin, 1996).

This monoclinic crystal is non-merohedrally twinned; the program ROTAX was used to find the twin law, which was [100, 0-10, -10-1] (Cooper et al., 2002). The final refinement resulted in a ratio of 0.8104 (14): 0.1896 (14) for the two domains, with a final wR2 = 0.085 and R1 = 0.031.


Compound (I) was purchased from Acros Organics, Geel, Belgium. X-ray quality crystals were obtained by evaporation from formic acid at room temperature. The solid-state (KBr) infrared spectrum of (I) features a single broad asymmetric peak at 1686 cm-1 for both C=O functions, typical of unstrained carboxyl-paired keto acids. In CHCl3 solution, this combined absorption is seen at the same wavenumber.


All H atoms for (I) were found in electron density difference maps. The fractional coordinates of the acid H was allowed to refine and its Uiso(H) was set at 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 phenyl Hs were constrained to ride on their parent C atoms with C—H distances of 0.95 Å and Uiso(H) = 1.2Ueq(C).


Fig. 1.
A view of the asymmetric unit of (I) with its numbering scheme. Displacement ellipsoids are drawn at the 40% probability level for non-H atoms.
Fig. 2.
A partial packing diagram showing the herringbone pattern of the two sets of dimers making up this structure. Displacement ellipsoids are drawn at the 40% probability level for non-H atoms. Hydrogen bonds are shown as dashed lines.

Crystal data

C9H8O3F(000) = 344
Mr = 164.15Dx = 1.427 Mg m3
Monoclinic, P21/cMelting point: 438 K
Hall symbol: -P 2ybcCu Kα radiation, λ = 1.54178 Å
a = 3.8202 (1) ÅCell parameters from 6415 reflections
b = 15.6478 (3) Åθ = 4.5–70.3°
c = 12.9282 (3) ŵ = 0.90 mm1
β = 98.508 (1)°T = 100 K
V = 764.31 (3) Å3Rod, colourless
Z = 40.20 × 0.18 × 0.11 mm

Data collection

Bruker SMART CCD APEXII area-detector diffractometer1386 independent reflections
Radiation source: fine-focus sealed tube1351 reflections with I > 2σ(I)
graphiteRint = 0.023
[var phi] and ω scansθmax = 71.0°, θmin = 2.8°
Absorption correction: numerical (SADABS; Sheldrick, 2008a)h = −4→4
Tmin = 0.840, Tmax = 0.907k = −18→18
7201 measured reflectionsl = −15→15


Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.031H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.085w = 1/[σ2(Fo2) + (0.0497P)2 + 0.2254P] where P = (Fo2 + 2Fc2)/3
S = 1.06(Δ/σ)max < 0.001
1386 reflectionsΔρmax = 0.18 e Å3
115 parametersΔρmin = −0.20 e Å3
0 restraintsExtinction correction: SHELXTL (Sheldrick, 2008b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0029 (9)

Special details

Experimental. 'crystal mounted on a Cryoloop using Paratone-N'
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

O10.7469 (3)0.37754 (6)0.50800 (7)0.0258 (3)
C10.1930 (4)0.17156 (8)0.35852 (10)0.0167 (3)
O20.2316 (3)0.09082 (6)0.51488 (7)0.0272 (3)
C20.3766 (3)0.23971 (8)0.41031 (10)0.0166 (3)
O3−0.0709 (3)0.03570 (6)0.36893 (7)0.0249 (3)
H3−0.127 (5)−0.0066 (12)0.4144 (14)0.037*
C30.4409 (3)0.31325 (8)0.35589 (10)0.0161 (3)
C40.3245 (4)0.31730 (8)0.24841 (10)0.0187 (3)
C50.1437 (4)0.24901 (9)0.19657 (10)0.0193 (3)
C60.0753 (4)0.17637 (8)0.25067 (10)0.0176 (3)
C70.1179 (4)0.09528 (8)0.41951 (11)0.0187 (3)
C80.6344 (4)0.38585 (8)0.41580 (11)0.0178 (3)
C90.6809 (4)0.46813 (8)0.35915 (10)0.0215 (3)

Atomic displacement parameters (Å2)

O10.0343 (6)0.0221 (5)0.0188 (5)−0.0065 (5)−0.0033 (5)0.0005 (4)
C10.0180 (6)0.0156 (7)0.0169 (7)0.0015 (5)0.0044 (6)−0.0002 (5)
O20.0430 (7)0.0222 (5)0.0149 (5)−0.0086 (5)−0.0009 (5)0.0019 (4)
C20.0175 (6)0.0192 (6)0.0131 (6)0.0018 (5)0.0026 (5)−0.0007 (5)
O30.0356 (6)0.0180 (5)0.0199 (5)−0.0088 (5)0.0001 (5)−0.0002 (4)
C30.0151 (6)0.0159 (6)0.0174 (6)0.0019 (5)0.0026 (5)−0.0004 (5)
C40.0198 (7)0.0168 (6)0.0195 (7)0.0005 (5)0.0029 (6)0.0029 (5)
C50.0210 (7)0.0228 (7)0.0134 (6)0.0014 (6)0.0005 (6)−0.0003 (5)
C60.0177 (7)0.0176 (6)0.0172 (7)−0.0011 (5)0.0013 (6)−0.0033 (5)
C70.0218 (7)0.0164 (6)0.0180 (7)−0.0007 (5)0.0031 (6)−0.0021 (5)
C80.0166 (6)0.0178 (7)0.0190 (7)0.0015 (5)0.0026 (6)−0.0011 (5)
C90.0230 (7)0.0166 (7)0.0241 (7)−0.0033 (6)0.0012 (6)0.0007 (5)

Geometric parameters (Å, °)

O1—C81.2128 (17)C3—C81.5057 (18)
C1—C21.3922 (19)C4—C51.3897 (19)
C1—C61.4022 (18)C4—H40.9500
C1—C71.4818 (18)C5—C61.3797 (19)
O2—C71.2471 (17)C5—H50.9500
C2—C31.3896 (19)C6—H60.9500
C2—H20.9500C8—C91.5047 (18)
O3—C71.2952 (17)C9—H9A0.9800
O3—H30.931 (19)C9—H9B0.9800
C3—C41.3963 (19)C9—H9C0.9800
C2—C1—C6120.11 (12)C5—C6—C1119.43 (12)
C2—C1—C7118.98 (11)C5—C6—H6120.3
C6—C1—C7120.89 (12)C1—C6—H6120.3
C3—C2—C1120.34 (12)O2—C7—O3123.04 (12)
C3—C2—H2119.8O2—C7—C1120.31 (12)
C1—C2—H2119.8O3—C7—C1116.64 (12)
C7—O3—H3110.9 (12)O1—C8—C9121.32 (12)
C2—C3—C4119.16 (12)O1—C8—C3120.02 (12)
C2—C3—C8118.33 (11)C9—C8—C3118.66 (11)
C4—C3—C8122.51 (12)C8—C9—H9A109.5
C5—C4—C3120.50 (12)C8—C9—H9B109.5
C6—C5—C4120.46 (12)H9A—C9—H9C109.5
C6—C1—C2—C30.7 (2)C7—C1—C6—C5178.73 (12)
C7—C1—C2—C3−177.89 (12)C2—C1—C7—O2−3.2 (2)
C1—C2—C3—C4−1.1 (2)C6—C1—C7—O2178.21 (13)
C1—C2—C3—C8178.83 (12)C2—C1—C7—O3176.16 (12)
C2—C3—C4—C50.6 (2)C6—C1—C7—O3−2.4 (2)
C8—C3—C4—C5−179.34 (13)C2—C3—C8—O14.06 (19)
C3—C4—C5—C60.3 (2)C4—C3—C8—O1−176.04 (14)
C4—C5—C6—C1−0.7 (2)C2—C3—C8—C9−175.43 (12)
C2—C1—C6—C50.1 (2)C4—C3—C8—C94.47 (19)

Hydrogen-bond geometry (Å, °)

O3—H3···O2i0.931 (19)1.69 (2)2.6124 (13)173.4 (17)
C9—H9A···O1ii0.982.573.5283 (17)167
C4—H4···O2iii0.952.593.3153 (16)133

Symmetry codes: (i) −x, −y, −z+1; (ii) −x+2, −y+1, −z+1; (iii) x, −y+1/2, z−1/2.


Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LH5054).


  • Borthwick, P. W. (1980). Acta Cryst. B36, 628–632.
  • Bruker (2005). SAINT Bruker AXS Inc., Madison, Wisconsin, USA.
  • Bruker (2006). APEX2 Bruker AXS Inc., Madison, Wisconsin, USA.
  • Cooper, R. I., Gould, R. O., Parsons, S. & Watkin, D. J. (2002). J. Appl. Cryst.35, 168–174.
  • Dobson, A. J. & Gerkin, R. E. (1996). Acta Cryst. C52, 3078–3081. [PubMed]
  • Lalancette, R. A., Malak, M. H. & Thompson, H. W. (2007). Acta Cryst. E63, o3640.
  • Sheldrick, G. M. (2008a). SADABS University of Göttingen, Germany.
  • Sheldrick, G. M. (2008b). Acta Cryst. A64, 112–122. [PubMed]

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