The E and Z isomers of 3-(benzoxazol-2-yl)­prop-2-enoic acid

The carboxyl­ic acid group and the double bond are coplanar in (E)-3-(benzoxazol-2-yl)­prop-2-enoic acid, C₁₀H₇NO₃, whereas in isomeric (Z)-3-(benzoxazol-2-yl)­prop-2-enoic acid, also C₁₀H₇NO₃, they are almost orthogonal. In both isomers, a strong O—H...N hydrogen bond, with the carboxyl­ic acid group as a donor and the pyridine-like N atom as an acceptor, and weak C—H...O interactions contribute to the observed supramolecular structures, which are completed by π–π stacking interactions between oxazole and benzenoid rings.

S1. Comment

γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system (CNS). It operates through three different classes of receptors, consisting of the ionotropic GABA_A and GABA_C receptors, and the G-protein coupled receptor GABA_B (Chebib & Johnston, 2000). Hypoactivity of the GABA neuronal function has been associated with neurological disorders such as epilepsy, Huntington's chorea, anxiety, sleep disorders and pain. AUTHOR: are you saying that pain is a neurological disorder? Can you be more specific? In contrast, GABA mediated hyperactivity has been suggested to be an important component of schizophrenic symptoms (Frølund et al., 2002). In order to pharmacologically characterize these receptors, recent studies on the synthesis and characterization of several GABA agonists (Chambers et al., 2003; Frølund et al., 1995) and antagonists (Frølund et al., 2002) have been undertaken. GABA is a conformationally flexible molecule, capable of adopting receptor subtype-specific conformations; in this context, we report the results of structural analyses of the E and Z geometric isomers of 3-(benzoxazolyl)-2-propenoic acid [(I—E) and (I—Z), respectively], which are analogues of GABA.

A one-pot synthesis was carried out by mixing equimolar quantities of maleic anhydride with o-aminophenol in THF. Careful regulation of the temperature to 323 K, using Ac₂O as catalyst, yielded isomer (I—Z); isomer (I—E) was obtained when the temperature was raised to 343 K and an excess of Ac₂O was used. It appears that isomer (I—Z) is the kinetic product and isomer (I—E) is the thermodynamic product, since the former is observed by thin-layer chromatography in the early stages of the reaction. The molecular structures of isomers (I—E) and (I—Z) are shown in Figs. 1 and 2, respectively, while selected geometric parameters are given in Table 1 and Table 3, respectively. The bond lengths and angles are very similar in the two isomers, as is the anti disposition of the double bond and the imine groups. However, the carboxy and benzoxazole groups are on opposite sides in (I—E) and on the same side in (I—Z).

AUTHOR: At some point, do you want to mention briefly the intramolecular C—H···O contact? The carboxy group in (I—E) is coplanar with the double bond, whereas in (I—Z) these groups are almost orthogonal [O1B—C1—C2—C3 = −4.1 (2) and 103.7 (3)°, respectively], in agreement with the conformation reported for other Z-propenoic acids (Stomberg et al., 1995). This conformational difference between the isomers determines the observed crystal packing structure (see below). Isomer (I—E) forms supramolecular sheets in the (102) plane through both strong (Steiner, 2002), and weak (Desiraju, 1996) hydrogen-bonding interactions. The hydrogen-bonding geometry for isomer (I—E) is listed in Table 2. The carboxylic acid donor and pyridine-like N-atom acceptor form a strong O1A—H1A···N3'ⁱ interaction [symmetry code: (i) x − 1, 1/2 − y, −1/2 + z], which is complemented by the weak C5'—H5'···O1Bⁱⁱ interaction [symmetry code: (ii) 1 − x, y − 1/2, 1/2 − z] between an aromatic H-atom donor and a carbonyl O-atom acceptor (Fig. 3).

Centrosymmetric sheets pack via π–π stacking interactions (Hunter et al., 1991; Singh & Thornton, 1990) between oxazole and benzenoid rings along the c axis. The mean intercentroid and interplanar distances [3.7070 (10) {or 3.707 (1)?} and 3.435 (s.u.?) Å, respectively] at the (1 − x, −y, −z) symmetry position, (iii), indicate a face-to-face π–π stacking arrangement, whereas the distances [4.4487 (11) and 3.38 (2) Å] at the (1 − x, −y, 1 − z) symmetry position, (iv), indicate a parallel displaced π–π stacking arrangement. The former arrangement is overwhelmingly preferred in the stacking of electron-rich and electron deficient aromatic rings, such as benzene and hexafluorobenzene, whose 1:1 complex has mean intercentroid and interplanar distances of 3.7 and 3.4 Å, respectively (Williams, 1993). The electron-deficient carbonyl C atom is located 3.42 (2) Å from the electron-rich double bond of the neighbouring molecule [symmetry code: (v) x, 1/2 − y, −1/2 + z], forming an angle of 68 (1)° with it (Fig. 3). This distance is as short as the sum of the van der Waals radii of two C atoms (3.4 Å; Hunter et al., 1991), and the carbonyl group is parallel but slightly slipped [displaced?] relative to the double bond. Therefore, this interaction can be considered as a paralled displaced olefin-type π–π stacking interaction (Kim et al., 2000), which should be an important contributor to the slippage of the hydrogen-bonded supramolecular sheets of isomer (I—E).

Molecules of (I—Z) are linked by a strong hydrogen-bonding interaction [O1A—H1A···N3'ⁱ; symmetry code: (i) 1/2 + x, 1/2 + y, z], between the carboxylic acid donor and pyridine-like N-atom acceptor, and a weak interaction [C3—H3···O1Bⁱⁱ; symmetry code: (ii) 1/2 − x, y − 1/2, 1/2 − z], involving a vinyl H-atom donor and the carbonyl O-atom acceptor (Fig. 4). As a consequence, a twisted eight-membered chain is formed, whose topological motif is described by the C(8)[C(7) C(5)] graph-set descriptor (Bernstein et al., 1995). This interaction is allowed because of the almost perpendicular conformation between the carboxy and the double-bond groups. The hydrogen-bonding geometry for isomer (I—Z) is listed in Table 4.

Centrosymmetric molecules of isomer (I—Z) also form π–π stacks, two almost perpendicular sets of columns developing in the [230] and [230] directions (Fig. 4). The mean intercentroid and interplanar distances between the oxazole [3.4727 (13) and 3.378 (s.u.?)Å; symmetry code: (iii) −x, 1 − y, −z] and benzenoid rings [3.5631 (14) and 3.310 (s.u.?) Å; symmetry code: (iv) 1/2 − x, 1/2 − y, −z] are also in the range expected for a face-to-face geometry (Hunter et al., 1991; Singh & Thornton, 1990), with less slippage than observed for isomer (I—E).

S2. Experimental

Propenoic acid derivatives (I—Z) and (I—E) were obtained by the reaction between equimolar quantities (1.0 mmol) of maleic anhydride and 2-aminophenol dissolved in tetrahydrofuran (THF). Ac₂O (0.1 mmol) was added as catalyst, and after heating at 323–328 K for 2 h, isomer (I—Z) was obtained. Under the same conditions, but heating at 343 K for 3 h, isomer (I—E) was obtained. In both cases, THF was removed by evaporation and the resulting solid was treated with aqueous HCl (5%) until precipitation was complete. After washing three times with deionized water and drying, the product was recrystallized from ethanol solutions to give crystals suitable for X-ray analysis in approximately 70% yield. For (I—E), m.p. 500–502 K; IR (KBr, cm⁻¹): ν 1710 (COO), 1527 (C=N); ¹H NMR: δ 13.2 (b, 1H, OH), 7.84 (d, 1H, ³J = 8.6 Hz, H4), 7.77 (d, 1H, ³J = 8.6 Hz, H7), 7.52 (dd, 1H, ³J = 8.6 Hz, H6), 7.45 (d, 1H, ³J = 15.8 Hz, H10), 7.44 (dd, 1H, ³J = 8.6 Hz, H5), 6.92 (d, 1H, ³J = 15.8 and 15.8 Hz, H11); ¹³C NMR: δ 166.0 (C12), 159.9 (C2), 150.1 (C8), 141.4 (C-9), 129.3 (C11), 128.2 (C10), 126.9 (C6), 125.2 (C5), 120.5 (C4), 111.1 (C7). For (I—Z), m.p. 396–397 K; IR (KBr, cm⁻¹): ν 1707 (COO), 1527 (C=N); ¹H NMR: δ 13.2 (b, 1H, OH), 7.8 (dd, 1H, ³J = 8.5 Hz, ⁴J = 1.2 Hz, H4), 7.7 (dd, 1H, ³J = 8.0 Hz, ⁴J = 1.3 Hz, H7), 7.4 (ddd, 1H, ³J = 8.6 Hz, ⁴J = 1.3 Hz, H6), 7.5 (ddd, 1H, ³J = 8.6 Hz, ⁴J = 1.3 Hz, H5), 6.88 (d, 1H, ³J = 12.0 Hz, H10), 6.66 (d, 1H, ³J = 12.0 Hz, H11); ¹³C NMR: δ 167.0 (C12), 159.6 (C2), 149.8 (C8), 140.1 (C9), 132.3 (C11), 120.0 (C10), 126.3 (C6), 125.1 (C5), 120.1 (C4), 111.0 (C7).

S3. Refinement

All H atoms were refined as riding on their parent atoms using SHELXL97 (Sheldrick, 1997) defaults [O—H = 0.82 Å, C—H = 0.9298–0.9301 Å and U_iso(H) = 1.2U_eq(C,O)] ##AUTHOR: Specify the X—H distances applied, and also the treatment of the U_iso values for H atoms. Here is an example from a different structure: # The NH H atoms were refined freely. Methyl H atoms attached to # sp² centres were located from difference Fourier syntheses and # refined as part of rigid rotating groups with C—H distances fixed # at 0.96 Å and U_iso(H) = 1.5U_eq(C). Other hydrogen atoms were # introduced at geometrically calculated positions and refined using # a riding model with fixed C—H bond lengths of 0.95 Å (sp² C—H) # or 0.99 Å (methylenes), and with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1992) for I-E; SMART (Bruker, 2000) for I-Z. Cell refinement: CAD-4 EXPRESS for I-E; SMART for I-Z. Data reduction: JANA98 (Vaclav, 1998) for I-E; SAINT (Bruker, 2000) for I-Z. For both compounds, program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997). Molecular graphics: WinGX (Farrugia, 1999) for I-E; SHELXTL (Bruker, 2000) for I-Z. Software used to prepare material for publication: SHELXL97 for I-E; SHELXL97 and WinGX2003 (Farrugia, 1999) for I-Z.

Figures

	Fig. 1. The molecular structure of (I—E), showing displacement ellipsoids at the 30% probability level.
	Fig. 2. The molecular structure of (I—Z), showing displacement ellipsoids at the 30% probability level.
	Fig. 3. The supramolecular structure of (I—E), viewed along the a axis. Centrosymmetric sheets of (I—E) pack through face-to-face and parallel-displaced π stacking interactions. [Symmetry codes: (i) x − 1, 1/2 − y, −1/2 + z; (ii) 1 − x, y − 1/2, 1/2 − z; (iii) 1 − x, −y, −z; (iv) 1 − x, −y, 1 − z; (v) x, 1/2 − y, 1/2 + z.]
	Fig. 4. The supramolecular structure of (I—Z), viewed along the a [230] and direction. AUTHOR: The previous sentence does not make sense - please clarify. [Symmetry codes: (i) 1/2 + x, 1/2 + y, z; (ii) 1/2 − x, y − 1/2, 1/2 − z; (iii) −x, 1 − y, −z.]

(I-E) (E)-3-(benzoxazol-2-yl)prop-2-enoic acid

Crystal data

C10H7NO3	F(000) = 392
Mr = 189.17	Dx = 1.449 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 24 reflections
a = 5.882 (1) Å	θ = 10–11°
b = 19.694 (1) Å	µ = 0.11 mm^−1
c = 7.4910 (1) Å	T = 293 K
β = 91.715 (10)°	Block, yellow
V = 867.37 (15) Å^3	0.50 × 0.50 × 0.40 mm
Z = 4

Data collection

Enraf–Nonius CAD-4 diffractometer	1554 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.011
Graphite monochromator	θmax = 28.0°, θmin = 2.9°
Detector resolution: 3 pixels mm^-1	h = −7→7
ω/2θ scans	k = 0→25
2082 measured reflections	l = 0→9
2082 independent 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) = 0.124	H-atom parameters constrained
S = 1.15	w = 1/[σ^2(Fo^2) + (0.058P)^2 + 0.105P] where P = (Fo^2 + 2Fc^2)/3
2082 reflections	(Δ/σ)max = 0.001
128 parameters	Δρmax = 0.19 e Å^−3
0 restraints	Δρmin = −0.18 e Å^−3

Special details

Experimental. Diffractometer operator Susana Rojas Lima scanwidth_degrees 0.7 low_scanspeed_degrees/min 16.1 high_scanspeed_degrees/min 60 Background measurement: Moving crystal and moving counter at the beginning and end of scan, each for 25% of total scan area. Crystal mounted on a glass fiber.

Melting points were measured on a Gallen-Kamp MFB-595 apparatus and are uncorrected. IR spectra were recorded as KBr discs using a Perkin-Elmer 16 F PC IR spectrophotometer. ¹H and ¹³C NMR spectra were recorded with a Jeol Eclipse (¹H, 270.17; 13 C, 67.94 MHz) instrument in CDCl₃ solutions, using SiMe₄ as internal reference and following standard techniques.

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All e.s.d.'s are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

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
O1'	0.19143 (16)	0.07791 (5)	0.12194 (13)	0.0441 (3)
O1A	−0.29352 (19)	0.26311 (5)	−0.11302 (17)	0.0577 (4)
O1B	−0.0045 (2)	0.32487 (6)	−0.00237 (17)	0.0641 (4)
N3'	0.50902 (19)	0.12704 (6)	0.23255 (15)	0.0422 (4)
C1	−0.0947 (3)	0.27108 (7)	−0.0281 (2)	0.0441 (4)
C2	0.0031 (3)	0.20497 (7)	0.02673 (19)	0.0457 (4)
C2'	0.3106 (2)	0.13587 (7)	0.15533 (18)	0.0403 (4)
C3	0.2083 (2)	0.19981 (7)	0.10092 (19)	0.0439 (4)
C4'	0.7046 (3)	0.01690 (8)	0.3240 (2)	0.0499 (5)
C5'	0.6701 (3)	−0.05243 (9)	0.3223 (2)	0.0565 (5)
C6'	0.4693 (3)	−0.08116 (8)	0.2545 (2)	0.0576 (5)
C7'	0.2940 (3)	−0.04194 (8)	0.1836 (2)	0.0523 (5)
C8'	0.3332 (2)	0.02687 (7)	0.18488 (17)	0.0411 (4)
C9'	0.5296 (2)	0.05681 (7)	0.25275 (18)	0.0401 (4)
H1A	−0.33657	0.29971	−0.15382	0.0693*
H2	−0.08278	0.16580	0.00838	0.0548*
H3	0.29201	0.23937	0.11937	0.0526*
H4'	0.83836	0.03594	0.37056	0.0599*
H5'	0.78435	−0.08075	0.36770	0.0677*
H6'	0.45266	−0.12810	0.25704	0.0691*
H7'	0.15924	−0.06075	0.13820	0.0627*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1'	0.0382 (5)	0.0384 (5)	0.0550 (6)	−0.0016 (4)	−0.0122 (4)	−0.0024 (4)
O1A	0.0458 (6)	0.0433 (6)	0.0825 (8)	−0.0007 (5)	−0.0233 (5)	0.0109 (5)
O1B	0.0646 (7)	0.0390 (6)	0.0869 (8)	−0.0044 (5)	−0.0257 (6)	−0.0010 (5)
N3'	0.0362 (6)	0.0403 (6)	0.0495 (7)	−0.0010 (5)	−0.0084 (5)	−0.0012 (5)
C1	0.0426 (7)	0.0389 (7)	0.0503 (8)	0.0006 (6)	−0.0076 (6)	0.0009 (5)
C2	0.0443 (7)	0.0372 (7)	0.0548 (8)	−0.0006 (6)	−0.0106 (6)	0.0005 (6)
C2'	0.0367 (7)	0.0388 (7)	0.0449 (7)	−0.0019 (5)	−0.0059 (5)	−0.0031 (5)
C3	0.0425 (7)	0.0374 (7)	0.0513 (7)	−0.0008 (5)	−0.0070 (6)	−0.0017 (6)
C4'	0.0416 (7)	0.0554 (9)	0.0524 (8)	0.0069 (6)	−0.0047 (6)	0.0051 (7)
C5'	0.0588 (10)	0.0547 (9)	0.0560 (9)	0.0185 (8)	0.0029 (7)	0.0098 (7)
C6'	0.0729 (11)	0.0396 (8)	0.0604 (9)	0.0056 (7)	0.0057 (8)	0.0027 (7)
C7'	0.0559 (9)	0.0414 (8)	0.0593 (9)	−0.0047 (7)	−0.0033 (7)	−0.0046 (6)
C8'	0.0413 (7)	0.0392 (7)	0.0425 (7)	0.0019 (5)	−0.0033 (5)	−0.0021 (5)
C9'	0.0375 (7)	0.0420 (7)	0.0407 (6)	0.0016 (5)	−0.0025 (5)	−0.0001 (5)

Geometric parameters (Å, º)

O1'—C2'	1.3588 (17)	C4'—C5'	1.380 (2)
O1'—C8'	1.3800 (16)	C5'—C6'	1.392 (2)
O1A—C1	1.324 (2)	C6'—C7'	1.382 (2)
O1B—C1	1.1978 (19)	C7'—C8'	1.375 (2)
O1A—H1A	0.8200	C8'—C9'	1.3804 (18)
N3'—C2'	1.2987 (17)	C2—H2	0.9300
N3'—C9'	1.3962 (18)	C3—H3	0.9298
C1—C2	1.477 (2)	C4'—H4'	0.9300
C2—C3	1.318 (2)	C5'—H5'	0.9299
C2'—C3	1.4489 (19)	C6'—H6'	0.9299
C4'—C9'	1.389 (2)	C7'—H7'	0.9301
O1A···C2^i	3.317 (2)	C5'···O1B^ix	3.372 (2)
O1A···N3'^ii	2.6995 (16)	C5'···C4'^viii	3.566 (2)
O1B···C3^i	3.295 (2)	C6'···C2'^vii	3.536 (2)
O1B···C2'^i	3.3004 (19)	C6'···C4'^viii	3.579 (2)
O1B···C5'^iii	3.372 (2)	C7'···C8'^vii	3.589 (2)
O1'···H2	2.4978	C7'···C9'^vii	3.471 (2)
O1'···H7'^iv	2.8152	C8'···C7'^vii	3.589 (2)
O1B···H5'^iii	2.4640	C9'···C7'^vii	3.471 (2)
O1B···H3	2.5717	C9'···C5'^viii	3.427 (2)
N3'···O1A^v	2.6995 (16)	C2'···H1A^v	2.7898
N3'···H1A^v	1.8932	C7'···H2^iv	3.0749
C1···C2^i	3.433 (2)	C9'···H1A^v	3.0102
C1···C3^i	3.395 (2)	H1A···N3'^ii	1.8932
C2···O1A^vi	3.317 (2)	H1A···C2'^ii	2.7898
C2···C1^vi	3.433 (2)	H1A···C9'^ii	3.0102
C2'···C6'^vii	3.536 (2)	H2···O1'	2.4978
C2'···O1B^vi	3.3004 (19)	H2···C7'^iv	3.0749
C3···O1B^vi	3.295 (2)	H2···H7'^iv	2.3788
C3···C1^vi	3.395 (2)	H3···O1B	2.5717
C4'···C5'^viii	3.566 (2)	H5'···O1B^ix	2.4640
C4'···C6'^viii	3.579 (2)	H7'···O1'^iv	2.8152
C5'···C9'^viii	3.427 (2)	H7'···H2^iv	2.3788
C2'—O1'—C8'	104.23 (10)	O1'—C8'—C7'	128.04 (12)
C1—O1A—H1A	109.47	N3'—C9'—C8'	108.32 (11)
C2'—N3'—C9'	104.76 (11)	C4'—C9'—C8'	120.15 (13)
O1A—C1—C2	111.12 (12)	N3'—C9'—C4'	131.53 (12)
O1B—C1—C2	124.61 (16)	C1—C2—H2	119.00
O1A—C1—O1B	124.25 (14)	C3—C2—H2	119.01
C1—C2—C3	121.98 (14)	C2—C3—H3	118.19
O1'—C2'—C3	118.08 (11)	C2'—C3—H3	118.22
N3'—C2'—C3	127.00 (12)	C5'—C4'—H4'	121.65
O1'—C2'—N3'	114.92 (12)	C9'—C4'—H4'	121.66
C2—C3—C2'	123.59 (13)	C4'—C5'—H5'	119.04
C5'—C4'—C9'	116.69 (15)	C6'—C5'—H5'	119.06
C4'—C5'—C6'	121.90 (16)	C5'—C6'—H6'	119.04
C5'—C6'—C7'	121.90 (15)	C7'—C6'—H6'	119.07
C6'—C7'—C8'	115.17 (15)	C6'—C7'—H7'	122.41
O1'—C8'—C9'	107.77 (12)	C8'—C7'—H7'	122.42
C7'—C8'—C9'	124.20 (13)
C8'—O1'—C2'—N3'	−0.41 (15)	N3'—C2'—C3—C2	−178.33 (14)
C2'—O1'—C8'—C7'	180.00 (17)	C5'—C4'—C9'—N3'	−179.50 (14)
C2'—O1'—C8'—C9'	0.04 (14)	C5'—C4'—C9'—C8'	0.0 (2)
C8'—O1'—C2'—C3	178.85 (11)	C9'—C4'—C5'—C6'	−0.7 (2)
C9'—N3'—C2'—O1'	0.59 (15)	C4'—C5'—C6'—C7'	0.6 (2)
C2'—N3'—C9'—C4'	179.06 (15)	C5'—C6'—C7'—C8'	0.1 (2)
C2'—N3'—C9'—C8'	−0.52 (15)	C6'—C7'—C8'—C9'	−0.8 (2)
C9'—N3'—C2'—C3	−178.60 (13)	C6'—C7'—C8'—O1'	179.29 (13)
O1A—C1—C2—C3	174.58 (14)	O1'—C8'—C9'—C4'	−179.35 (12)
O1B—C1—C2—C3	−4.1 (3)	C7'—C8'—C9'—N3'	−179.64 (13)
C1—C2—C3—C2'	−179.56 (13)	C7'—C8'—C9'—C4'	0.7 (2)
O1'—C2'—C3—C2	2.5 (2)	O1'—C8'—C9'—N3'	0.29 (14)

Symmetry codes: (i) x, −y+1/2, z−1/2; (ii) x−1, −y+1/2, z−1/2; (iii) −x+1, y+1/2, −z+1/2; (iv) −x, −y, −z; (v) x+1, −y+1/2, z+1/2; (vi) x, −y+1/2, z+1/2; (vii) −x+1, −y, −z; (viii) −x+1, −y, −z+1; (ix) −x+1, y−1/2, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1A—H1A···N3′^ii	0.82	1.89	2.6995 (16)	167
C2—H2···O1′	0.93	2.50	2.8196 (18)	100
C5′—H5′···O1B^ix	0.93	2.46	3.372 (2)	165

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

(I-Z) (E)-3-(benzoxazol-2-yl)prop-2-enoic acid

Crystal data

C10H7NO3	F(000) = 784
Mr = 189.17	Dx = 1.414 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 1010 reflections
a = 9.8191 (19) Å	θ = 1.6–32.0°
b = 9.905 (2) Å	µ = 0.11 mm^−1
c = 18.320 (4) Å	T = 293 K
β = 94.037 (4)°	Block, yellow
V = 1777.4 (6) Å^3	0.36 × 0.21 × 0.19 mm
Z = 8

Data collection

Bruker SMART area-detector diffractometer	Rint = 0.035
Graphite monochromator	θmax = 27.5°, θmin = 2.2°
ϕ and ω scans	h = −12→12
9736 measured reflections	k = −12→12
2013 independent reflections	l = −23→23
1559 reflections with I > 2σ(I)

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)] = 0.053	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.127	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.045P)^2 + 1.031P] where P = (Fo^2 + 2Fc^2)/3
2013 reflections	(Δ/σ)max < 0.001
128 parameters	Δρmax = 0.23 e Å^−3
0 restraints	Δρmin = −0.18 e Å^−3

Special details

Experimental. Diffractometer operator H. Höpfl scanwidth_degrees 0.7 low_scanspeed_degrees/min 16.1 high_scanspeed_degrees/min 60 Background measurement: Moving crystal and moving counter at the beginning and end of scan, each for 25% of total scan area. Crystal mounted on a glass fiber.

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All e.s.d.'s are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

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
O1'	0.22231 (13)	0.47504 (12)	0.05292 (7)	0.0486 (4)
O1A	0.48568 (14)	0.57351 (13)	0.13708 (8)	0.0615 (5)
O1B	0.33365 (18)	0.71816 (15)	0.17534 (9)	0.0801 (6)
N3'	0.11006 (14)	0.28418 (15)	0.07418 (9)	0.0482 (5)
C1	0.3773 (2)	0.60559 (19)	0.17063 (10)	0.0488 (6)
C2	0.3145 (2)	0.4896 (2)	0.20736 (10)	0.0538 (7)
C2'	0.18735 (18)	0.38027 (17)	0.10189 (10)	0.0455 (6)
C3	0.2335 (2)	0.39429 (19)	0.17792 (10)	0.0522 (6)
C4'	0.0151 (2)	0.2510 (2)	−0.05751 (13)	0.0645 (8)
C5'	0.0144 (2)	0.3112 (3)	−0.12498 (14)	0.0748 (9)
C6'	0.0841 (2)	0.4301 (3)	−0.13600 (12)	0.0710 (9)
C7'	0.1591 (2)	0.4950 (2)	−0.08002 (11)	0.0599 (7)
C8'	0.15859 (18)	0.43348 (19)	−0.01291 (10)	0.0463 (6)
C9'	0.08944 (18)	0.31515 (19)	−0.00027 (11)	0.0481 (6)
H1A	0.51842	0.64177	0.12002	0.0738*
H2	0.33476	0.48313	0.25759	0.0645*
H3	0.20327	0.32945	0.20973	0.0627*
H4'	−0.03199	0.17117	−0.05044	0.0774*
H5'	−0.03436	0.27086	−0.16452	0.0898*
H6'	0.08024	0.46736	−0.18269	0.0852*
H7'	0.20654	0.57467	−0.08721	0.0719*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1'	0.0533 (7)	0.0395 (7)	0.0540 (8)	−0.0028 (5)	0.0104 (6)	0.0039 (5)
O1A	0.0614 (9)	0.0454 (8)	0.0803 (10)	−0.0028 (7)	0.0232 (7)	0.0067 (7)
O1B	0.0997 (12)	0.0521 (9)	0.0929 (12)	0.0068 (8)	0.0371 (10)	−0.0028 (8)
N3'	0.0427 (8)	0.0393 (8)	0.0640 (10)	0.0004 (7)	0.0142 (7)	−0.0005 (7)
C1	0.0562 (11)	0.0468 (11)	0.0433 (10)	−0.0030 (9)	0.0037 (8)	−0.0051 (8)
C2	0.0600 (12)	0.0590 (12)	0.0433 (10)	0.0000 (10)	0.0105 (8)	0.0050 (9)
C2'	0.0442 (9)	0.0373 (9)	0.0565 (11)	0.0019 (8)	0.0150 (8)	0.0044 (8)
C3	0.0569 (11)	0.0472 (10)	0.0545 (11)	−0.0013 (9)	0.0173 (9)	0.0093 (9)
C4'	0.0487 (11)	0.0621 (13)	0.0823 (16)	0.0029 (10)	0.0025 (10)	−0.0165 (12)
C5'	0.0585 (13)	0.0961 (19)	0.0682 (15)	0.0169 (13)	−0.0067 (11)	−0.0203 (13)
C6'	0.0613 (14)	0.0942 (19)	0.0571 (13)	0.0239 (13)	0.0019 (10)	0.0049 (12)
C7'	0.0568 (12)	0.0618 (13)	0.0619 (12)	0.0130 (10)	0.0093 (10)	0.0107 (10)
C8'	0.0419 (9)	0.0449 (10)	0.0527 (11)	0.0097 (8)	0.0070 (8)	−0.0013 (8)
C9'	0.0392 (9)	0.0466 (10)	0.0596 (12)	0.0088 (8)	0.0105 (8)	−0.0040 (9)

Geometric parameters (Å, º)

O1'—C2'	1.359 (2)	C4'—C5'	1.372 (4)
O1'—C8'	1.382 (2)	C5'—C6'	1.384 (4)
O1A—C1	1.305 (2)	C6'—C7'	1.379 (3)
O1B—C1	1.200 (2)	C7'—C8'	1.373 (3)
O1A—H1A	0.8199	C8'—C9'	1.382 (3)
N3'—C2'	1.298 (2)	C2—H2	0.9299
N3'—C9'	1.399 (3)	C3—H3	0.9298
C1—C2	1.487 (3)	C4'—H4'	0.9296
C2—C3	1.324 (3)	C5'—H5'	0.9299
C2'—C3	1.441 (3)	C6'—H6'	0.9299
C4'—C9'	1.389 (3)	C7'—H7'	0.9304
O1'···O1A	3.075 (2)	C5'···C2'^i	3.490 (3)
O1'···C1	2.859 (2)	C5'···C3^i	3.398 (3)
O1'···C4'^i	3.411 (2)	C6'···C2'^vi	3.355 (3)
O1A···O1'	3.075 (2)	C7'···O1B^iv	3.338 (3)
O1A···N3'^ii	2.715 (2)	C7'···N3'^vi	3.438 (3)
O1B···C3^iii	3.310 (3)	C7'···C9'^vi	3.487 (3)
O1B···C7'^iv	3.338 (3)	C8'···C9'^vi	3.503 (3)
O1A···H2^v	2.6748	C8'···C8'^vi	3.445 (3)
O1B···H3^iii	2.4264	C8'···N3'^i	3.380 (2)
O1B···H7'^iv	2.6237	C8'···C9'^i	3.487 (3)
N3'···C7'^vi	3.438 (3)	C9'···C8'^i	3.487 (3)
N3'···O1A^vii	2.715 (2)	C9'···C7'^vi	3.487 (3)
N3'···C8'^i	3.380 (2)	C9'···C8'^vi	3.503 (3)
N3'···H1A^vii	1.9003	C9'···C9'^i	3.406 (3)
C1···O1'	2.859 (2)	C9'···C2'^i	3.548 (3)
C2'···C6'^vi	3.355 (3)	C2'···H1A^vii	2.9189
C2'···C9'^i	3.548 (3)	C9'···H1A^vii	2.9169
C2'···C4'^i	3.350 (3)	H1A···N3'^ii	1.9003
C2'···C5'^i	3.490 (3)	H1A···C2'^ii	2.9189
C3···O1B^viii	3.310 (3)	H1A···C9'^ii	2.9169
C3···C5'^i	3.398 (3)	H2···O1A^v	2.6748
C4'···C2'^i	3.350 (3)	H3···O1B^viii	2.4264
C4'···O1'^i	3.411 (2)	H7'···O1B^iv	2.6237
C2'—O1'—C8'	104.51 (13)	O1'—C8'—C7'	128.29 (17)
C1—O1A—H1A	109.47	N3'—C9'—C8'	108.07 (16)
C2'—N3'—C9'	105.13 (15)	C4'—C9'—C8'	119.99 (18)
O1A—C1—C2	113.76 (16)	N3'—C9'—C4'	131.94 (18)
O1B—C1—C2	121.59 (18)	C1—C2—H2	115.75
O1A—C1—O1B	124.57 (18)	C3—C2—H2	115.74
C1—C2—C3	128.51 (17)	C2—C3—H3	116.50
O1'—C2'—C3	119.65 (15)	C2'—C3—H3	116.54
N3'—C2'—C3	125.74 (17)	C5'—C4'—H4'	121.61
O1'—C2'—N3'	114.59 (16)	C9'—C4'—H4'	121.61
C2—C3—C2'	126.97 (17)	C4'—C5'—H5'	118.99
C5'—C4'—C9'	116.8 (2)	C6'—C5'—H5'	119.00
C4'—C5'—C6'	122.0 (2)	C5'—C6'—H6'	118.90
C5'—C6'—C7'	122.1 (2)	C7'—C6'—H6'	118.96
C6'—C7'—C8'	115.08 (19)	C6'—C7'—H7'	122.46
O1'—C8'—C9'	107.70 (16)	C8'—C7'—H7'	122.47
C7'—C8'—C9'	124.01 (18)
C8'—O1'—C2'—N3'	0.4 (2)	N3'—C2'—C3—C2	178.51 (19)
C2'—O1'—C8'—C7'	178.88 (19)	C5'—C4'—C9'—N3'	178.7 (2)
C2'—O1'—C8'—C9'	−0.49 (19)	C5'—C4'—C9'—C8'	−0.3 (3)
C8'—O1'—C2'—C3	−178.08 (16)	C9'—C4'—C5'—C6'	0.0 (3)
C9'—N3'—C2'—O1'	−0.1 (2)	C4'—C5'—C6'—C7'	0.4 (4)
C2'—N3'—C9'—C4'	−179.3 (2)	C5'—C6'—C7'—C8'	−0.4 (3)
C2'—N3'—C9'—C8'	−0.17 (19)	C6'—C7'—C8'—C9'	0.1 (3)
C9'—N3'—C2'—C3	178.23 (17)	C6'—C7'—C8'—O1'	−179.18 (18)
O1A—C1—C2—C3	−79.5 (3)	O1'—C8'—C9'—C4'	179.66 (16)
O1B—C1—C2—C3	103.7 (3)	C7'—C8'—C9'—N3'	−178.98 (17)
C1—C2—C3—C2'	0.4 (3)	C7'—C8'—C9'—C4'	0.3 (3)
O1'—C2'—C3—C2	−3.2 (3)	O1'—C8'—C9'—N3'	0.4 (2)

Symmetry codes: (i) −x+1/2, −y+1/2, −z; (ii) x+1/2, y+1/2, z; (iii) −x+1/2, y+1/2, −z+1/2; (iv) −x+1/2, −y+3/2, −z; (v) −x+1, y, −z+1/2; (vi) −x, −y+1, −z; (vii) x−1/2, y−1/2, z; (viii) −x+1/2, y−1/2, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1A—H1A···N3′^ii	0.82	1.90	2.715 (2)	172
C3—H3···O1B^viii	0.93	2.43	3.310 (3)	159

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