2-Oxo-2-(2-thien­yl)acetic acid

The structure of the title compound, C₆H₄O₃S, displays inter­molecular hydrogen-bonding dimers. The structure exhibits a thienyl-ring flip disorder of the main mol­ecule [occupancy ratio = 91.3 (2):8.7 (2)].

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• Disorder in main residue
• R factor = 0.037
• wR factor = 0.106
• Data-to-parameter ratio = 18.5

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT934_ALERT_3_B Number of (Iobs-Icalc)/SigmaW .gt. 10 Outliers .          1

Alert level C
PLAT230_ALERT_2_C Hirshfeld Test Diff for    S1     --  C6      ..       5.67 su
PLAT369_ALERT_2_C Long   C(sp2)-C(sp2) Bond  C1     -   C2     ...       1.54 Ang.
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          3
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          1
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600        209

Alert level G
PLAT301_ALERT_3_G Note: Main Residue  Disorder ...................      33.00 Perc.
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......         12
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K
PLAT811_ALERT_5_G No ADDSYM Analysis: Too Many Excluded Atoms ....          !

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   5 ALERT level C = Check and explain
   5 ALERT level G = General alerts; check

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   5 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. Comment

The structure of 2-oxo-2-(2-thienyl)acetic acid, C₆H₄O₃S, has monoclinic (P2₁/c) symmetry. The structure displays intermolecular hydrogen bonding dimers. The structure exhibits a thienyl-ring flip disorder of the main molecule.

The structure of the title compound displays centrosymmetric R₂²(8) dimers by a simple O—H···O interactions (Bernstein et al., 1995). The structure exhibits a thienyl-ring flip disorder of the main molecule with occupancy ratios of 91.3 (2)% to 8.7 (2)%.

Related literature

For a discussion of ring-flip disorder in unsubstituted 2- and 3-thienyl rings, see: Crundwell et al. (2003). For related literature [please provide some indication of what these references refer to], Steel & Fitchett (2000, 2006).

For related literature, see: Spek (2009).

S2. Experimental

The title compound was purchased as 2-thiopheneglyoxylic acid from Aldrich (95% purity). Crystals for this x-ray diffraction study were harvested from methanol during routine recrystallization.

S3. Refinement

During refinement, the thienyl ring showed evidence of ring-flip disorder which is common for unsubstituted 2- and 3-thienyl rings (Crundwell et al., 2003). After finding three of the flipped disordered atoms in the difference map, the rest of the ring was generated and modeled. The final model suggested that the thienyl ring disorder was 8.7 (2)%.

Hydrogen atoms on carbons were included in calculated positions with a C—H distance of 0.93 Å and were included in the refinement in riding motion approximation with U_iso = 1.2U_eq of the carrier atom.

The hydroxyl hydrogen was included in a calculated position with a O—H distance of 0.82 Å and was included in the refinement in riding motion approximation with U_iso = 1.2U_eq of the carrier atom.

Computing details

Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO (Oxford Diffraction, 2009); data reduction: CrysAlis PRO (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

Fig. 1. A view of the title compound (Farrugia, 1997). Displacement ellipsoids are drawn at the 50% probability level.

2-Oxo-2-(2-thienyl)acetic acid

Crystal data

C6H4O3S	F(000) = 320
Mr = 156.15	Dx = 1.687 Mg m^−3
Monoclinic, P21/c	Melting point: 361 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 3.7481 (10) Å	Cell parameters from 6632 reflections
b = 15.314 (3) Å	θ = 3.8–32.0°
c = 10.727 (3) Å	µ = 0.46 mm^−1
β = 93.30 (2)°	T = 293 K
V = 614.7 (3) Å^3	Plate, yellow
Z = 4	0.34 × 0.21 × 0.11 mm

Data collection

Oxford Diffraction Xcalibur Sapphire3 diffractometer	1927 independent reflections
Radiation source: Enhance (Mo) X-ray Source	1512 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
Detector resolution: 16.1790 pixels mm^-1	θmax = 32.0°, θmin = 3.8°
ω scans	h = −5→5
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009)	k = −22→16
Tmin = 0.944, Tmax = 1.000	l = −15→15
6475 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.106	H-atom parameters constrained
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0678P)^2 + 0.018P] where P = (Fo^2 + 2Fc^2)/3
1927 reflections	(Δ/σ)max = 0.002
104 parameters	Δρmax = 0.51 e Å^−3
12 restraints	Δρmin = −0.29 e Å^−3

Special details

Experimental. Hydrogen atoms on carbons were included in calculated positions with a C—H distance of 0.93 Å and were included in the refinement in riding motion approximation with U_iso = 1.2U_eq of the carrier atom.

The hydroxyl hydrogen was included in a calculated position with a O—H distance of 0.82 Å and was included in the refinement in riding motion approximation with U_iso = 1.2U_eq of the carrier atom.

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	0.1858 (3)	0.98317 (6)	0.36658 (10)	0.0261 (3)
H1	0.2759	1.0208	0.4128	0.039*
O2	0.5095 (3)	0.89316 (7)	0.49326 (9)	0.0207 (2)
C1	0.2916 (4)	0.90590 (8)	0.40596 (12)	0.0167 (3)
C2	0.1123 (4)	0.83170 (8)	0.32857 (12)	0.0156 (3)
O3	−0.0839 (3)	0.85113 (7)	0.23733 (9)	0.0207 (2)
C3	0.1813 (3)	0.74199 (8)	0.36784 (12)	0.0153 (3)	0.9131 (17)
C4	0.3362 (8)	0.70703 (19)	0.4767 (2)	0.0176 (4)	0.9131 (17)
H4	0.4368	0.7412	0.5413	0.021*	0.9131 (17)
C5	0.3282 (10)	0.61491 (14)	0.4812 (2)	0.0158 (3)	0.9131 (17)
H5	0.4176	0.5815	0.5484	0.019*	0.9131 (17)
C6	0.1687 (5)	0.58091 (10)	0.37166 (15)	0.0158 (3)	0.9131 (17)
H6	0.1417	0.5214	0.3564	0.019*	0.9131 (17)
S1	0.02766 (10)	0.65987 (2)	0.26826 (3)	0.01633 (14)	0.9131 (17)
C3B	0.1813 (3)	0.74199 (8)	0.36784 (12)	0.0153 (3)	0.0869 (17)
C4B	0.057 (4)	0.6842 (10)	0.2959 (14)	0.01633 (14)	0.0869 (17)
H4B	−0.0609	0.6947	0.2187	0.020*	0.0869 (17)
C5B	0.122 (6)	0.5982 (11)	0.350 (2)	0.0158 (3)	0.0869 (17)
H5B	0.0539	0.5454	0.3127	0.019*	0.0869 (17)
C6B	0.303 (13)	0.6081 (13)	0.464 (3)	0.0158 (3)	0.0869 (17)
H6B	0.3739	0.5612	0.5151	0.019*	0.0869 (17)
S1B	0.384 (3)	0.7158 (6)	0.5057 (7)	0.0176 (4)	0.0869 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0349 (6)	0.0124 (4)	0.0291 (6)	0.0006 (4)	−0.0140 (4)	−0.0003 (4)
O2	0.0264 (5)	0.0153 (5)	0.0193 (5)	0.0004 (4)	−0.0080 (4)	−0.0003 (4)
C1	0.0180 (6)	0.0151 (6)	0.0170 (6)	−0.0003 (5)	0.0004 (5)	−0.0007 (5)
C2	0.0166 (6)	0.0150 (6)	0.0152 (6)	0.0009 (5)	−0.0005 (4)	−0.0003 (5)
O3	0.0245 (5)	0.0203 (5)	0.0166 (5)	0.0016 (4)	−0.0060 (4)	0.0009 (4)
C3	0.0159 (6)	0.0132 (6)	0.0165 (6)	0.0006 (5)	−0.0005 (5)	−0.0015 (5)
C4	0.0204 (11)	0.0172 (9)	0.0147 (13)	−0.0002 (7)	−0.0017 (9)	−0.0020 (9)
C5	0.0181 (9)	0.0144 (7)	0.0147 (10)	0.0001 (6)	−0.0009 (7)	−0.0009 (6)
C6	0.0160 (8)	0.0128 (7)	0.0184 (8)	0.0012 (6)	−0.0017 (6)	0.0023 (6)
S1	0.0178 (2)	0.0142 (2)	0.0167 (2)	−0.00080 (14)	−0.00148 (14)	−0.00162 (13)
C3B	0.0159 (6)	0.0132 (6)	0.0165 (6)	0.0006 (5)	−0.0005 (5)	−0.0015 (5)
C4B	0.0178 (2)	0.0142 (2)	0.0167 (2)	−0.00080 (14)	−0.00148 (14)	−0.00162 (13)
C5B	0.0160 (8)	0.0128 (7)	0.0184 (8)	0.0012 (6)	−0.0017 (6)	0.0023 (6)
C6B	0.0181 (9)	0.0144 (7)	0.0147 (10)	0.0001 (6)	−0.0009 (7)	−0.0009 (6)
S1B	0.0204 (11)	0.0172 (9)	0.0147 (13)	−0.0002 (7)	−0.0017 (9)	−0.0020 (9)

Geometric parameters (Å, º)

O1—C1	1.3102 (16)	C5—C6	1.389 (2)
O1—H1	0.8200	C5—H5	0.9300
O2—C1	1.2223 (16)	C6—S1	1.7041 (15)
C1—C2	1.5387 (19)	C6—H6	0.9300
C2—O3	1.2265 (17)	C4B—C5B	1.452 (16)
C2—C3	1.4558 (18)	C4B—H4B	0.9300
C3—C4	1.382 (3)	C5B—C6B	1.380 (17)
C3—S1	1.7272 (13)	C5B—H5B	0.9300
C4—C5	1.412 (3)	C6B—S1B	1.730 (18)
C4—H4	0.9300	C6B—H6B	0.9300
C1—O1—H1	109.5	C6—C5—H5	124.6
O2—C1—O1	124.58 (12)	C4—C5—H5	124.6
O2—C1—C2	123.18 (12)	C5—C6—S1	112.77 (15)
O1—C1—C2	112.23 (11)	C5—C6—H6	123.6
O3—C2—C3	123.25 (12)	S1—C6—H6	123.6
O3—C2—C1	118.33 (12)	C6—S1—C3	91.96 (7)
C3—C2—C1	118.42 (11)	C5B—C4B—H4B	124.7
C4—C3—C2	132.00 (15)	C6B—C5B—C4B	108.5 (16)
C4—C3—S1	110.46 (14)	C6B—C5B—H5B	125.8
C2—C3—S1	117.44 (10)	C4B—C5B—H5B	125.8
C3—C4—C5	114.04 (18)	C5B—C6B—S1B	113.7 (16)
C3—C4—H4	123.0	C5B—C6B—H6B	123.1
C5—C4—H4	123.0	S1B—C6B—H6B	123.1
C6—C5—C4	110.76 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2^i	0.82	1.82	2.637 (2)	176

Symmetry code: (i) −x+1, −y+2, −z+1.