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The title monohydrate, C7H10O3·H2O, aggregates as a complex hydrogen-bonding network, in which the water mol­ecule accepts a hydrogen bond from the carboxyl group of one mol­ecule and donates hydrogen bonds to ketone and carboxyl C=O functions in two additional mol­ecules, yielding a sheet-like structure of parallel ribbons. The keto acid adopts a chiral conformation through rotation of the carboxyl group by 62.50 (15)° relative to the plane defined by its point of attachment and the ketone C and O atoms. Two C—H...O close contacts exist in the structure.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103029329/fr1456sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270103029329/fr1456Isup2.hkl
Contains datablock I

CCDC reference: 233136

Comment top

Our studies of the crystallography of ketocarboxylic acids explore the molecular characteristics that control their hydrogen bonding. Beyond their five known hydrogen-bonding modes, keto acids sometimes occur as hydrates, with complex hydrogen-bonding patterns that typically involve both ketone and acid carbonyl groups. The title compound crystallizes as a monohydrate, (I), with such a pattern of hydrogen bonding. Although hydrate examples are known in which the ketone function is as far as 12 atoms away from the carboxyl group, a large preponderance of known hydrates are either γ- or, like the present case, δ-keto acids.

Fig. 1 shows the asymmetric unit of (I). Although the organic portion lacks inherent chirality, it adopts a chiral conformation through rotation of its carboxyl unit about the C1—C7 bond, the only conformational option available. This group is turned so that the C1—C2 bond coincides with the carboxyl plane [O2—C7—C1—C2 = 2.0 (4)°]. The dihedral angle ?between the planes the ketone (O1/C3–C5) and the carboxyl (O2/O3/C7/C1) planes is? 48.91 (13)°. The water moelcule, which donates hydrogen bonds to atoms O1 and O2 in separate molecules, is shown here in its relationship to atom O3, from which it accepts a hydrogen bond.

The partial averaging of C—O bond lengths and C—C—O angles by disorder often seen in acids is unique to the carboxyl-pairing hydrogen-bonding mode, whose geometry permits transposition of the two carboxyl O atoms. As in other hydrates that involve the acid, no significant averaging is observed for (I), whose bond lengths are 1.206 (3) and 1.326 (3) Å, with angles of 124.5 (2) and 113.4 (2)°. Our own survey of 56 keto acid structures that are not acid dimers gives average values of 1.200 (10) and 1.32 (2) Å, and 124.5 (14) and 112.7 (17)°, for these lengths and angles, in accordance with typical values of 1.21 and 1.31 Å, and 123 and 112°, cited for highly ordered dimeric carboxyls (Borthwick, 1980).

Fig. 2 illustrates the packing of the cell and the hydrogen-bonding network. The latter does not incorporate any water-to-water hydrogen bonds (cf. Brunskill et al., 2001); however, in an arrangement identical in its essentials to at least two previously reported cases (Lalancette et al., 1990, 1997), the water molecule accepts a hydrogen bond from the carboxyl group of one molecule and donates hydrogen bonds to ketone and acid C=O functions in two separate molecules. This produces three-bond intermolecular connections of both the acid-to-water-to-acid and acid-to-water-to-ketone type, plus a four-bond acid-to-water-to-ketone connection, all of which lie in a two-dimensional sheet of separate, parallel, ribbon-like structures. This structure may be contrasted with instances bearing exactly the same types of connections, which produce structures that are three-dimensional rather than lamellar (Thompson & Lalancette, 2001; Lalancette et al., 2002).

We characterize the geometry of hydrogen bonding to carbonyls using a combination of the H···O=C angle and the H···O=C—C torsion angle. These describe the approach of the H atom to the O atom in terms of its deviation from, respectively, C=O axiality (ideal = 120°) and planarity with the carbonyl group (ideal = 0°). In (I), the H···O=C and H···O=C—C angles are 145.2 (10) and 85.0 (16)° for the water-to-acid hydrogen bond, and 122.7 (9) and 8.5 (11)° for the water-to-ketone hydrogen bond. In particular, the 85.0° value departs dramatically from the supposed `ideal' value of 0°. The O···O distances in this hydrogen-bonding network all lie within normal parameters, between 2.606 (3) and 2.797 (3) Å.

Intermolecular C—H···O close contacts were found for the acid carbonyl (2.56 Å to atom H6B in a centrosymmetrically related molecule) and for the water molecule (2.69 Å to atom H2B in a molecule translationally related in b). These distances lie within the 2.7 Å range we standardly employ for non-bonded H···O packing interactions (Steiner, 1997). Using compiled data for a large number of C—H···O contacts, Steiner & Desiraju (1998) find significant statistical directionality, even as far away as 3.0 Å, and conclude that these are legitimately viewed as `weak hydrogen bonds,' with a greater contribution to packing forces than simple van der Waals attractions.

The solid-state (KBr) infrared spectrum of the hydrate (I) displays a single broadened C=O absorption at 1702 cm−1 for both the acid and the ketone. In CHCl3 solution, where dimers predominate, a single absorption is centered at 1711 cm−1.

Experimental top

Compound (I) was synthesized by catalytic hydrogenation of an ethanol solution of p-hydroxybenzoic acid over a rhodium catalyst; Jones oxidation of the resulting oil yielded crystalline material. Crystals of the monohydrate (I) suitable for X-ray diffraction (m.p. 336 K), were obtained from diethyl ether/hexane mixtures. The anhydrous form has also been reported (Perkin, 1904; Hardegger et al., 1944; Applequist & Klieman, 1961), although its melting point (341 K) is so close to that of (I) that in some reports one cannot tell which form was present. Combustion analyses of the anhydrate seem always to err on the low-carbon side, suggesting, as we have found, that this material hydrates easily.

Refinement top

All H atoms were found in electron-density difference maps. C-bound H atoms were placed in calculated positions (0.98 Å for methylene H atoms and 0.99 Å for the methine H atoms) and allowed to refine as riding on their respective C atoms; their displacement parameters were allowed to refine. The hydroxy and water H atoms were not constrained positionally, and their displacement parameters were allowed to refine.

Computing details top

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXP97 (Sheldrick, 1997); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The asymmetric unit for (I); the water of hydration is shown, arbitrarily, in its relation to the carboxyl OH group. Displacement ellipsoids are shown at the 20% probability level.
[Figure 2] Fig. 2. A packing diagram, with the cell contents and extra molecules, including several water molecules, to clarify the hydrogen bonding. For clarity, all C-bound H atoms have been omitted. Displacement ellipsoids are shown at the 20% probability level.
'4-Oxocyclohexanecarboxylic acid' top
Crystal data top
C7H10O3·H2OZ = 2
Mr = 160.17F(000) = 172
Triclinic, P1Dx = 1.324 Mg m3
Hall symbol: -P 1Melting point: 336 K
a = 6.7298 (8) ÅMo Kα radiation, λ = 0.71073 Å
b = 7.2091 (11) ÅCell parameters from 19 reflections
c = 8.4367 (12) Åθ = 3.8–9.9°
α = 85.928 (13)°µ = 0.11 mm1
β = 83.075 (17)°T = 243 K
γ = 82.132 (16)°Flat plate, colourless
V = 401.88 (10) Å30.45 × 0.45 × 0.02 mm
Data collection top
Siemens P4
diffractometer
Rint = 0.023
Radiation source: fine-focus sealed tubeθmax = 25.0°, θmin = 2.4°
Graphite monochromatorh = 71
2θ/θ scansk = 88
1798 measured reflectionsl = 1010
1405 independent reflections3 standard reflections every 97 reflections
920 reflections with I > 2σ(I) intensity decay: variation <1.2%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.045Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.105H atoms treated by a mixture of independent and constrained refinement
S = 1.03 w = 1/[σ2(Fo2) + (0.0363P)2 + 0.0971P]
where P = (Fo2 + 2Fc2)/3
1405 reflections(Δ/σ)max < 0.001
121 parametersΔρmax = 0.15 e Å3
0 restraintsΔρmin = 0.14 e Å3
Crystal data top
C7H10O3·H2Oγ = 82.132 (16)°
Mr = 160.17V = 401.88 (10) Å3
Triclinic, P1Z = 2
a = 6.7298 (8) ÅMo Kα radiation
b = 7.2091 (11) ŵ = 0.11 mm1
c = 8.4367 (12) ÅT = 243 K
α = 85.928 (13)°0.45 × 0.45 × 0.02 mm
β = 83.075 (17)°
Data collection top
Siemens P4
diffractometer
Rint = 0.023
1798 measured reflections3 standard reflections every 97 reflections
1405 independent reflections intensity decay: variation <1.2%
920 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0450 restraints
wR(F2) = 0.105H atoms treated by a mixture of independent and constrained refinement
S = 1.03Δρmax = 0.15 e Å3
1405 reflectionsΔρmin = 0.14 e Å3
121 parameters
Special details top

Experimental. 'crystal mounted on glass fiber using epoxy resin, then coated in the epoxy resin'

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) top
xyzUiso*/Ueq
O11.0337 (3)0.9393 (2)0.6954 (2)0.0480 (5)
O20.2689 (3)0.6172 (3)0.9440 (2)0.0518 (5)
O30.3376 (3)0.4398 (3)0.7352 (2)0.0540 (6)
H30.238 (5)0.369 (5)0.796 (4)0.095 (12)*
O40.0903 (3)0.2231 (3)0.8886 (3)0.0504 (5)
H420.020 (5)0.271 (4)0.943 (4)0.084 (12)*
H410.057 (5)0.133 (4)0.830 (4)0.075 (10)*
C10.5063 (3)0.7084 (3)0.7261 (3)0.0338 (6)
H1A0.45020.76230.62720.045 (7)*
C20.5307 (4)0.8706 (3)0.8256 (3)0.0417 (7)
H2A0.58360.82050.92550.064 (9)*
H2B0.39840.94310.85310.061 (8)*
C30.6740 (4)1.0002 (3)0.7356 (4)0.0492 (7)
H3A0.61081.06630.64520.083 (11)*
H3B0.69751.09430.80720.060 (8)*
C40.8722 (4)0.8929 (3)0.6750 (3)0.0381 (6)
C50.8585 (4)0.7227 (4)0.5869 (3)0.0489 (7)
H5A0.99280.65050.56950.054 (8)*
H5B0.81390.76240.48200.065 (9)*
C60.7117 (4)0.5964 (3)0.6776 (3)0.0413 (7)
H6A0.69450.49640.60960.054 (8)*
H6B0.76840.53790.77360.046 (7)*
C70.3594 (4)0.5870 (3)0.8142 (3)0.0354 (6)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0407 (11)0.0522 (11)0.0540 (11)0.0162 (9)0.0021 (9)0.0089 (9)
O20.0525 (12)0.0607 (12)0.0396 (11)0.0114 (10)0.0144 (9)0.0103 (9)
O30.0579 (13)0.0617 (13)0.0475 (11)0.0316 (11)0.0094 (10)0.0178 (10)
O40.0379 (12)0.0522 (12)0.0631 (13)0.0165 (10)0.0058 (10)0.0157 (10)
C10.0343 (14)0.0365 (13)0.0315 (13)0.0066 (11)0.0043 (11)0.0032 (11)
C20.0301 (14)0.0408 (14)0.0541 (17)0.0023 (12)0.0000 (12)0.0154 (13)
C30.0463 (16)0.0362 (14)0.0668 (19)0.0048 (13)0.0085 (15)0.0118 (14)
C40.0431 (16)0.0383 (14)0.0339 (14)0.0141 (12)0.0006 (12)0.0011 (11)
C50.0503 (17)0.0544 (16)0.0437 (17)0.0220 (14)0.0129 (13)0.0150 (13)
C60.0420 (15)0.0385 (14)0.0422 (15)0.0103 (12)0.0105 (12)0.0097 (12)
C70.0306 (14)0.0410 (14)0.0350 (14)0.0053 (11)0.0031 (11)0.0042 (12)
Geometric parameters (Å, º) top
O1—C41.215 (3)C2—H2A0.9800
O2—C71.206 (3)C2—H2B0.9800
O3—C71.326 (3)C3—C41.499 (4)
O3—H30.97 (4)C3—H3A0.9800
O4—H420.87 (4)C3—H3B0.9800
O4—H410.91 (3)C4—C51.498 (3)
C1—C71.505 (3)C5—C61.535 (3)
C1—C21.524 (3)C5—H5A0.9800
C1—C61.528 (3)C5—H5B0.9800
C1—H1A0.9900C6—H6A0.9800
C2—C31.533 (4)C6—H6B0.9800
C7—O3—H3109.6 (19)H3A—C3—H3B108.0
H42—O4—H41107 (3)O1—C4—C5121.7 (2)
C7—C1—C2110.83 (19)O1—C4—C3122.9 (2)
C7—C1—C6112.07 (19)C5—C4—C3115.4 (2)
C2—C1—C6110.28 (19)C4—C5—C6112.5 (2)
C7—C1—H1A107.8C4—C5—H5A109.1
C2—C1—H1A107.8C6—C5—H5A109.1
C6—C1—H1A107.8C4—C5—H5B109.1
C1—C2—C3111.7 (2)C6—C5—H5B109.1
C1—C2—H2A109.3H5A—C5—H5B107.8
C3—C2—H2A109.3C1—C6—C5111.2 (2)
C1—C2—H2B109.3C1—C6—H6A109.4
C3—C2—H2B109.3C5—C6—H6A109.4
H2A—C2—H2B107.9C1—C6—H6B109.4
C4—C3—C2111.6 (2)C5—C6—H6B109.4
C4—C3—H3A109.3H6A—C6—H6B108.0
C2—C3—H3A109.3O2—C7—O3122.1 (2)
C4—C3—H3B109.3O2—C7—C1124.5 (2)
C2—C3—H3B109.3O3—C7—C1113.4 (2)
C7—C1—C2—C3178.0 (2)C7—C1—C6—C5179.6 (2)
C6—C1—C2—C357.4 (3)C2—C1—C6—C556.4 (3)
C1—C2—C3—C452.8 (3)C4—C5—C6—C151.8 (3)
C2—C3—C4—O1131.1 (3)C2—C1—C7—O22.0 (4)
C2—C3—C4—C548.9 (3)C6—C1—C7—O2125.7 (3)
O1—C4—C5—C6131.2 (3)C2—C1—C7—O3177.8 (2)
C3—C4—C5—C648.7 (3)C6—C1—C7—O354.2 (3)

Experimental details

Crystal data
Chemical formulaC7H10O3·H2O
Mr160.17
Crystal system, space groupTriclinic, P1
Temperature (K)243
a, b, c (Å)6.7298 (8), 7.2091 (11), 8.4367 (12)
α, β, γ (°)85.928 (13), 83.075 (17), 82.132 (16)
V3)401.88 (10)
Z2
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.45 × 0.45 × 0.02
Data collection
DiffractometerSiemens P4
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
1798, 1405, 920
Rint0.023
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.045, 0.105, 1.03
No. of reflections1405
No. of parameters121
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.15, 0.14

Computer programs: XSCANS (Siemens, 1996), XSCANS, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXP97 (Sheldrick, 1997), SHELXL97.

Selected geometric parameters (Å, º) top
O2—C71.206 (3)O3—C71.326 (3)
O2—C7—C1124.5 (2)O3—C7—C1113.4 (2)
 

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