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Acta Crystallogr Sect E Struct Rep Online. 2009 April 1; 65(Pt 4): o937.
Published online 2009 March 31. doi:  10.1107/S1600536809010708
PMCID: PMC2969029

(±)-2-Oxocyclo­penta­neacetic acid: catemeric hydrogen bonding in a γ-keto acid


The title racemate, C7H10O3, aggregates in the solid as acid-to-ketone hydrogen-bonding catemers [O(...)O = 2.7050 (13) Å and O—H(...)O = 166.1 (17)°] having glide-related components. Four such heterochiral chains, paired centrosymmetrically about (An external file that holds a picture, illustration, etc.
Object name is e-65-0o937-efi1.jpg, An external file that holds a picture, illustration, etc.
Object name is e-65-0o937-efi1.jpg, An external file that holds a picture, illustration, etc.
Object name is e-65-0o937-efi1.jpg) in the cell, proceed through the cell in the 010 direction, with alignment with respect to the c axis of ++−−.

Related literature

For background to catemers and hydrogen bonds, see: Barcon et al. (1998 [triangle], 2002 [triangle]); Coté et al. (1996 [triangle]); DeVita Dufort et al. (2007 [triangle]); Efthimiopoulos et al. (2009 [triangle]); Harata et al. (1977 [triangle]); Lalancette & Thompson (2003 [triangle]); Lalancette et al. (2006 [triangle]); Malak et al. (2006 [triangle]); Newman et al. (2002 [triangle]); Steiner (1997 [triangle]); Stork et al. (1963 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-65-0o937-scheme1.jpg


Crystal data

  • C7H10O3
  • M r = 142.15
  • Orthorhombic, An external file that holds a picture, illustration, etc.
Object name is e-65-0o937-efi4.jpg
  • a = 5.3232 (1) Å
  • b = 12.2981 (3) Å
  • c = 20.8148 (5) Å
  • V = 1362.65 (5) Å3
  • Z = 8
  • Cu Kα radiation
  • μ = 0.91 mm−1
  • T = 100 K
  • 0.37 × 0.15 × 0.10 mm

Data collection

  • Bruker SMART CCD APEXII area-detector diffractometer
  • Absorption correction: multi-scan (SADABS; Sheldrick, 2008a [triangle]) T min = 0.730, T max = 0.915
  • 9810 measured reflections
  • 1197 independent reflections
  • 1147 reflections with I > 2σ(I)
  • R int = 0.016


  • R[F 2 > 2σ(F 2)] = 0.033
  • wR(F 2) = 0.086
  • S = 1.04
  • 1197 reflections
  • 95 parameters
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 0.26 e Å−3
  • Δρmin = −0.15 e Å−3

Data collection: APEX2 (Bruker, 2006 [triangle]); cell refinement: SAINT (Bruker, 2006 [triangle]); data reduction: SAINT; 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/S1600536809010708/fl2241sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809010708/fl2241Isup2.hkl

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


HWT is grateful to Professor Gree Loober Spoog for helpful consultations. The authors acknowledge support by NSF-CRIF grant No. 0443538. EG and HWT express their gratitude to Sanofi–Aventis for a grant in support of undergraduate research in organic synthesis. This paper is dedicated to the memory of HWT; he was a dedicated mentor, teacher and friend at Rutgers University-Newark for over 40 years.

supplementary crystallographic information


Our study of the crystal structures of ketocarboxylic acids explores their five known H-bonding modes. Two of these do not involve the ketone, corresponding to the common pairing and much rarer chain modes in simple acids. Acid-to-ketone chains (catemers) constitute a sizable overall minority of cases, while acid-to-ketone dimers and intramolecular H-bonds are rarely observed. We have presented examples of many of these and have discussed factors that contribute to the choice of mode (Coté et al., 1996; Newman et al., 2002; Lalancette et al., 2006; DeVita Dufort et al., 2007).

An issue of interest is the minimum requirements for catemer formation. However, the very smallest molecules offer several experimental problems (volatility, low crystallinity, little structural variability), so that few C3—C6 keto-acids have been previously reported (Harata et al., 1977; Malak et al., 2006; Efthimiopoulos et al., 2009). We now report the crystal structure of the title C7γ-keto acid (I), among the smallest found to aggregate in the solid as a catemer. The category of γ-keto acids is especially rich in H-bonding types, embracing internal H bonds and catemers of the screw, translation and glide types, as well as dimers and hydrated patterns. The intra-chain glide relationship found is considerably rarer than either screw or translational schemes generally, and is shared with three other γ-keto acids of our experience (Barcon et al., 1998, 2002; DeVita Dufort et al., 2007).

Fig. 1 presents a view of the asymmetric unit of (I) with its numbering. The conformation adopted by the ring involves flexing of the two ring-carbons most remote from the ketone, C4 & C5, so as to place them farthest from the average ring-plane, -0.2218 (9) & 0.2424 (9) Å, respectively, on opposite faces of the ring. This permits staggering of all ring-H atoms and projects the side-chain pseudo-equatorially, with a O1—C2—C1—C6 torsion angle of 32.63 (17)°.

In solution, full rotation about both C—C bonds in the side-chain is possible; however, in the solid the staggering requirements about C1—C6 allow few real options. The observed C2—C1—C6—C7 torsion angle of 57.31 (14)° places the carboxyl group maximally away from the ring plane, and the carboxyl is rotated so that its carbonyl is essentially coplanar with the C1—C6 bond [O2—C7—C6—C1 = -7.31 (18)°]. The intramolecular dihedral angle between the carboxyl and ketone planes is 75.03 (5)°.

Averaging of C—O bond lengths and C—C—O angles by disorder, although common in carboxyl dimers, is not seen in acid-to-ketone catemers, whose geometry cannot support any of the averaging mechanisms required. In (I) these C—O bonds have lengths of 1.2082 (15) & 1.3292 (15) Å, with angles of 125.09 (11) & 110.72 (10)°, similar to those in other fully ordered carboxylic acids.

Fig. 2 shows the packing of the cell and the parallel carboxyl-to-ketone H-bonding chains, all passing through the cell in the 010 direction. The chain components are glide-related with O···O distances of 2.7050 (13) Å, and O—H···O angles of 166.1 (17)°. The intermolecular dihedral angle for the acid versus ketone planes is 29.04 (8) °. Among H-bonding catemers, the observed prevalence of subtypes, describing the relation of adjacent molecules, is homochiral (screw > translation) > heterochiral (glide). The four heterochiral H-bonding chains in (I) are paired centrosymmetrically about 1/2, 1/2, 1/2, with each enantiomer in the array appearing four times. Starting at the origin, the order of the directional alignment of the four chains with respect to the c axis is + + - -.

We characterize the geometry of H bonding to carbonyls by a combination of H···O=C angle and H···O=C—C torsion angle. These describe the approach of the acid H-atom to the O in terms of its deviation from, respectively, C=O axiality (ideal = 120°) and planarity with the carbonyl (ideal = 0°). In (I) the values for these two angles are 125.2 (5) & -10.2 (7)°. No intermolecular C—H···O contacts were found within the 2.6 Å range we routinely survey for such close non-bonded polar interactions (Steiner, 1997).

Among the factors disfavoring standard dimeric carboxyl H bonding, we have identified low availability of alternative conformations. The conformational flexibility associated with cyclopentane rings is a solution characteristic; in the crystal, the requirements disfavoring hydrogen eclipsing and favoring pseudo-equatorial substituents leaves a system like (I) with few actual conformational options. As a result (I) joins a number of nominally flexible cyclic molecules we have found that behave much more like rigid systems and adopt catemeric H-bonding modes (Barcon et al., 2002; Malak et al., 2006; Lalancette & Thompson, 2003).

Because of the similar shifts produced by ketone ring-strain and by H bonding, the solid-state versus liquid IR spectra of carboxycyclopentanones are typically ambiguous regarding H bonding in the crystal. The solid-state (KBr) spectrum of (I) has C=O stretching absorptions at 1735 (acid) and 1721 cm-1 (ketone), consistent with known shifts produced when H-bonding is removed from carboxyl C=O and added to a ketone. In CHCl3 solution these peaks appear, presumably reversed, at 1736 and 1714 cm-1.


The ethyl ester of 2-oxocyclopentaneacetic acid, prepared via the enamine (Stork et al., 1963), was hydrolyzed by refluxing with conc. HCl. Distilled keto acid was recrystallized from ether-hexane to give material suitable for X-ray, mp 327 K.


All H atoms for (I) were found in electron density difference maps. The carboxyl H was refined positionally with 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).


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 packing diagram, illustrating the four heterochiral catemers created by acid-to-ketone H bonds proceeding along chains of molecules glide-related in the 010 direction. The handedness of the molecules is differentiated by the shading of the bonds. Starting ...

Crystal data

C7H10O3Dx = 1.386 Mg m3
Mr = 142.15Melting point: 327 K
Orthorhombic, PbcaCu Kα radiation, λ = 1.54178 Å
Hall symbol: -P 2ac 2abCell parameters from 7778 reflections
a = 5.3232 (1) Åθ = 4.3–67.1°
b = 12.2981 (3) ŵ = 0.91 mm1
c = 20.8148 (5) ÅT = 100 K
V = 1362.65 (5) Å3Needle, colourless
Z = 80.37 × 0.15 × 0.10 mm
F(000) = 608

Data collection

Bruker SMART CCD APEXII area-detector diffractometer1197 independent reflections
Radiation source: fine-focus sealed tube1147 reflections with I > 2σ(I)
graphiteRint = 0.016
[var phi] and ω scansθmax = 67.0°, θmin = 4.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 2008a)h = −6→6
Tmin = 0.730, Tmax = 0.915k = −14→14
9810 measured reflectionsl = −24→24


Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.033H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.086w = 1/[σ2(Fo2) + (0.0444P)2 + 0.8053P] where P = (Fo2 + 2Fc2)/3
S = 1.04(Δ/σ)max < 0.001
1197 reflectionsΔρmax = 0.26 e Å3
95 parametersΔρmin = −0.15 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: 0.0014 (4)

Special details

Experimental. Crystal mounted on a 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.

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

O11.12228 (17)0.12579 (7)0.31120 (4)0.0196 (3)
C10.7561 (2)0.03606 (10)0.35627 (6)0.0156 (3)
C20.9814 (2)0.11135 (10)0.35642 (6)0.0156 (3)
O21.16880 (17)−0.11081 (7)0.37021 (4)0.0205 (3)
O31.00596 (18)−0.22599 (7)0.29778 (4)0.0193 (3)
H31.131 (4)−0.2640 (14)0.3061 (8)0.029*
C30.9997 (2)0.16595 (11)0.42143 (6)0.0209 (3)
C40.7603 (3)0.13271 (11)0.45681 (6)0.0213 (3)
C50.6948 (2)0.02124 (11)0.42777 (6)0.0192 (3)
C60.7852 (2)−0.06445 (10)0.31485 (6)0.0154 (3)
C71.0077 (2)−0.13453 (10)0.33180 (6)0.0142 (3)

Atomic displacement parameters (Å2)

O10.0220 (5)0.0169 (5)0.0198 (5)−0.0025 (4)0.0027 (4)0.0010 (3)
C10.0140 (6)0.0151 (6)0.0176 (6)0.0018 (5)−0.0010 (5)0.0005 (5)
C20.0164 (6)0.0123 (6)0.0180 (6)0.0026 (5)−0.0013 (5)0.0027 (5)
O20.0191 (5)0.0196 (5)0.0228 (5)0.0020 (4)−0.0054 (4)−0.0024 (4)
O30.0194 (5)0.0143 (5)0.0241 (5)0.0027 (4)−0.0031 (4)−0.0034 (3)
C30.0230 (7)0.0206 (7)0.0192 (7)−0.0038 (5)−0.0008 (5)−0.0026 (5)
C40.0227 (7)0.0220 (7)0.0191 (7)0.0001 (5)0.0015 (5)−0.0034 (5)
C50.0182 (6)0.0200 (6)0.0192 (6)−0.0015 (5)0.0036 (5)−0.0013 (5)
C60.0148 (6)0.0150 (6)0.0163 (6)−0.0014 (5)−0.0011 (5)0.0002 (5)
C70.0150 (6)0.0134 (6)0.0141 (6)−0.0026 (5)0.0028 (5)0.0020 (4)

Geometric parameters (Å, °)

O1—C21.2165 (15)C3—H3A0.9900
C1—C21.5150 (17)C3—H3B0.9900
C1—C61.5150 (16)C4—C51.5383 (18)
C1—C51.5345 (17)C4—H4A0.9900
C2—C31.5138 (17)C5—H5A0.9900
O2—C71.2082 (15)C5—H5B0.9900
O3—C71.3292 (15)C6—C71.5066 (17)
O3—H30.832 (19)C6—H6A0.9900
C3—C41.5276 (18)C6—H6B0.9900
C2—C1—C6114.76 (10)C3—C4—H4B111.0
C2—C1—C5103.82 (10)C5—C4—H4B111.0
C6—C1—C5118.47 (10)H4A—C4—H4B109.0
C2—C1—H1106.3C1—C5—C4103.12 (10)
O1—C2—C3125.94 (11)C1—C5—H5B111.1
O1—C2—C1125.14 (11)C4—C5—H5B111.1
C3—C2—C1108.91 (10)H5A—C5—H5B109.1
C7—O3—H3111.1 (12)C7—C6—C1114.45 (10)
C2—C3—C4104.97 (10)C7—C6—H6A108.6
H3A—C3—H3B108.8O2—C7—O3124.18 (11)
C3—C4—C5103.78 (10)O2—C7—C6125.09 (11)
C3—C4—H4A111.0O3—C7—C6110.72 (10)
C6—C1—C2—O132.63 (17)C2—C1—C5—C434.53 (12)
C5—C1—C2—O1163.49 (12)C6—C1—C5—C4163.15 (11)
C6—C1—C2—C3−147.97 (11)C3—C4—C5—C1−39.41 (12)
C5—C1—C2—C3−17.11 (13)C2—C1—C6—C757.31 (14)
O1—C2—C3—C4172.13 (12)C5—C1—C6—C7−66.02 (14)
C1—C2—C3—C4−7.26 (13)C1—C6—C7—O2−7.31 (18)
C2—C3—C4—C528.73 (13)C1—C6—C7—O3173.81 (10)

Hydrogen-bond geometry (Å, °)

O3—H3···O1i0.832 (19)1.890 (19)2.7050 (13)166.1 (17)

Symmetry codes: (i) −x+5/2, y−1/2, z.


Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FL2241).


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