Crystal structure of (E)-pent-2-enoic acid

The mol­ecule of the title compound, C₅H₈O₂, a low-melting α,β-unsaturated carb­oxy­lic acid, is essentially planar [maximum displacement = 0.0239 (13) Å]. In the crystal, mol­ecules are linked into centrosymmetric dimers via pairs of O—H⋯O hydrogen bonds.

1. Related literature

For the synthesis of unsaturated carb­oxy­lic acids including the title compound, see: Shabtai et al. (1981); Gastaminza et al. (1984); Outurquin & Paulmier (1989). For crystal structure determinations of acrylic acid, see: Higgs & Sass (1963); Chatani et al. (1963); Boese et al. (1999); Oswald & Urquhart (2011). For the structure of crotonic acid, see: Shimizu et al. (1974). For the structure of related hexenoic acid cocrystals, see: Aakeröy et al. (2003); Stanton & Bak (2008).

2. Experimental

2.1. Crystal data

• C₅H₈O₂

• M_r = 100.11

• Triclinic,

• a = 6.7336 (13) Å

• b = 6.7821 (13) Å

• c = 7.2349 (14) Å

• α = 67.743 (2)°

• β = 75.518 (2)°

• γ = 64.401 (2)°

• V = 274.29 (9) ų

• Z = 2

• Mo Kα radiation

• μ = 0.09 mm⁻¹

• T = 150 K

• 0.51 × 0.35 × 0.27 mm

2.2. Data collection

• Bruker APEXII CCD diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2014) T_min = 0.81, T_max = 0.97

• 7544 measured reflections

• 1323 independent reflections

• 1122 reflections with I > 2σ(I)

• R_int = 0.026

2.3. Refinement

• R[F² > 2σ(F²)] = 0.037

• wR(F²) = 0.113

• S = 1.10

• 1323 reflections

• 69 parameters

• H atoms treated by a mixture of independent and constrained refinement

• Δρ_max = 0.36 e Å⁻³

• Δρ_min = −0.19 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯O2^i	0.95 (2)	1.69 (2)	2.6322 (13)	173.3 (19)
Symmetry code: (i) -x+1, -y+2, -z+1.

Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT (Bruker, 2013); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXL2014; software used to prepare material for publication: SHELXL2014.

Supporting information

S1. Synthesis and crystallization

Malonic acid (24.8 g, 237.8 mmol, 1eq) was dissolved in dry pyridine (37.6 g, 475.7 mmol, 2 eq) at room temperature in a three-necked flask equipped with a magnetic stir bar and a reflux condenser under a mild flow of argon. Propanal (13.8 g, 240.2 mmol, 1 eq) was then added in one portion and the resulting clear solution further stirred for 72 h at room temperature under argon. Afterwards, the resulting light yellow to orange solution was brought to an acidic pH value by adding phospho­ric acid at 0°C (42.5 wt.-%, 582.7 mmol, 2.45 eq). The resulting two layers were extracted three times with 150 mL portions of ethyl acetate and reduced to a volume of ca. 150 mL. To remove impurities from aldol condensation the raw acid was converted into the corresponding sodium salt by addition of an aqueous solution of sodium carbonate (18.9 g, 178.4 mmol, 0.75 eq in 200 mL). After stirring for 30 minutes the water phase was separated und extracted three times with 150 mL portions of ethyl acetate. The water phase was then acidified with concentrated hydro­chloric acid (35.2 g, 356.7 mmol, 1.5 eq), the organic phase was separated and the water phase was again extracted three times with 150 mL portions of ethyl acetate. The combined organic phases were dried over Na₂SO₄ and evaporated to dryness under diminished pressure. The resulting raw product was further purified by distillation in vacuo yielding the product in purity >99% (GC). M. p. 10°C. ¹H NMR (400 MHz, CDCl₃): δ = 12.35 (br s, 1H, OH); 7.14 (dt, ³J = 15.6 Hz, ³J = 6.3 Hz, 1H, -CH-); 5.82 (dt, ³J = 15.6 Hz, ⁴J = 1.7 Hz, 1H, -CH-); 2.30-2.21 (m, 2H, -CH₂-); 1.08 (t, ³J = 7.4 Hz, 3H, -CH₃-). ¹³C NMR (100 MHz, CDCl₃): δ = 172.69 (CO); 153.77 (CH); 119.76 (CH); 25.54 (CH₂); 21.10 (CH₃). MS (EI, 70 eV): m/z = 100 (M⁺, 50), 83 (13), 82 (23), 81 (10), 58 (11), 57 (17), 56 (23), 55 (100), 54 (43), 53 (35), 52 (12), 51 (25), 50 (28), 45 (77), 41 (36), 40 (13), 39 (99), 38 (25), 37 (11), 29 (61). HRMS (ESI-TOF/MS): calculated for C₅H₈O₂ (M⁺) 99.04515, found 99.04529. Elemental analysis for C₅H₈O₂ % (calc.): C 59.99 (59.98); H 8.05 (8.05). Suitable single crystals were grown by slow evaporation of an ethano­lic solution at -30 °C over one week.

S2. Refinement

The carb­oxy­lic H atom could be found in a difference Fourier map and was refined freely. All other H atoms were placed in idealized positions with d(C—H) = 0.95 Å (CH), 0.99 Å (CH₂), 0.98 Å (CH₃) and refined using a riding model with U_iso(H) fixed at 1.2 U_eq(C) for CH and CH₂ and 1.5 U_eq(C) for CH₃. A rotating model was used for the methyl group.

Related literature

For the synthesis of unsaturated carboxylic acids including the title compound, see: Shabtai et al. (1981); Gastaminza et al. (1984); Outurquin & Paulmier (1989). For crystal structure determinations of acrylic acid, see: Higgs & Sass (1963); Chatani et al. (1963); Boese et al. (1999); Oswald & Urquhart (2011). For the structure of crotonic acid, see: Shimizu et al. (1974). For the structure of related hexenoic acid cocrystals, see: Aakeröy et al. (2003); Stanton & Bak (2008).

Structure description

For the synthesis of unsaturated carboxylic acids including the title compound, see: Shabtai et al. (1981); Gastaminza et al. (1984); Outurquin & Paulmier (1989). For crystal structure determinations of acrylic acid, see: Higgs & Sass (1963); Chatani et al. (1963); Boese et al. (1999); Oswald & Urquhart (2011). For the structure of crotonic acid, see: Shimizu et al. (1974). For the structure of related hexenoic acid cocrystals, see: Aakeröy et al. (2003); Stanton & Bak (2008).

Synthesis and crystallization

Malonic acid (24.8 g, 237.8 mmol, 1eq) was dissolved in dry pyridine (37.6 g, 475.7 mmol, 2 eq) at room temperature in a three-necked flask equipped with a magnetic stir bar and a reflux condenser under a mild flow of argon. Propanal (13.8 g, 240.2 mmol, 1 eq) was then added in one portion and the resulting clear solution further stirred for 72 h at room temperature under argon. Afterwards, the resulting light yellow to orange solution was brought to an acidic pH value by adding phospho­ric acid at 0°C (42.5 wt.-%, 582.7 mmol, 2.45 eq). The resulting two layers were extracted three times with 150 mL portions of ethyl acetate and reduced to a volume of ca. 150 mL. To remove impurities from aldol condensation the raw acid was converted into the corresponding sodium salt by addition of an aqueous solution of sodium carbonate (18.9 g, 178.4 mmol, 0.75 eq in 200 mL). After stirring for 30 minutes the water phase was separated und extracted three times with 150 mL portions of ethyl acetate. The water phase was then acidified with concentrated hydro­chloric acid (35.2 g, 356.7 mmol, 1.5 eq), the organic phase was separated and the water phase was again extracted three times with 150 mL portions of ethyl acetate. The combined organic phases were dried over Na₂SO₄ and evaporated to dryness under diminished pressure. The resulting raw product was further purified by distillation in vacuo yielding the product in purity >99% (GC). M. p. 10°C. ¹H NMR (400 MHz, CDCl₃): δ = 12.35 (br s, 1H, OH); 7.14 (dt, ³J = 15.6 Hz, ³J = 6.3 Hz, 1H, -CH-); 5.82 (dt, ³J = 15.6 Hz, ⁴J = 1.7 Hz, 1H, -CH-); 2.30-2.21 (m, 2H, -CH₂-); 1.08 (t, ³J = 7.4 Hz, 3H, -CH₃-). ¹³C NMR (100 MHz, CDCl₃): δ = 172.69 (CO); 153.77 (CH); 119.76 (CH); 25.54 (CH₂); 21.10 (CH₃). MS (EI, 70 eV): m/z = 100 (M⁺, 50), 83 (13), 82 (23), 81 (10), 58 (11), 57 (17), 56 (23), 55 (100), 54 (43), 53 (35), 52 (12), 51 (25), 50 (28), 45 (77), 41 (36), 40 (13), 39 (99), 38 (25), 37 (11), 29 (61). HRMS (ESI-TOF/MS): calculated for C₅H₈O₂ (M⁺) 99.04515, found 99.04529. Elemental analysis for C₅H₈O₂ % (calc.): C 59.99 (59.98); H 8.05 (8.05). Suitable single crystals were grown by slow evaporation of an ethano­lic solution at -30 °C over one week.

Refinement details

The carb­oxy­lic H atom could be found in a difference Fourier map and was refined freely. All other H atoms were placed in idealized positions with d(C—H) = 0.95 Å (CH), 0.99 Å (CH₂), 0.98 Å (CH₃) and refined using a riding model with U_iso(H) fixed at 1.2 U_eq(C) for CH and CH₂ and 1.5 U_eq(C) for CH₃. A rotating model was used for the methyl group.

Computing details

Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT (Bruker, 2013); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXL2014 (Sheldrick, 2015); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015).

Figures

	Fig. 1. The molecular structure of the title compound with displacement ellipsoids drawn at 50% probability level.
	Fig. 2. ORTEP representation of a dimer formed by intermolecular O—H···O hydrogen bonds.

(E)-Pent-2-enoic acid

Crystal data

C5H8O2	Z = 2
Mr = 100.11	F(000) = 108
Triclinic, P1	Dx = 1.212 Mg m^−3
a = 6.7336 (13) Å	Mo Kα radiation, λ = 0.71073 Å
b = 6.7821 (13) Å	Cell parameters from 4399 reflections
c = 7.2349 (14) Å	θ = 3.1–28.7°
α = 67.743 (2)°	µ = 0.09 mm^−1
β = 75.518 (2)°	T = 150 K
γ = 64.401 (2)°	Prism, colourless
V = 274.29 (9) Å^3	0.51 × 0.35 × 0.27 mm

Data collection

Bruker APEXII CCD diffractometer	1323 independent reflections
Radiation source: fine-focus sealed tube	1122 reflections with I > 2σ(I)
Detector resolution: 8.3333 pixels mm^-1	Rint = 0.026
φ and ω scans	θmax = 28.0°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Bruker, 2014)	h = −8→8
Tmin = 0.81, Tmax = 0.97	k = −8→8
7544 measured reflections	l = −9→9

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F^2 > 2σ(F^2)] = 0.037	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.113	w = 1/[σ^2(Fo^2) + (0.0562P)^2 + 0.0602P] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max < 0.001
1323 reflections	Δρmax = 0.36 e Å^−3
69 parameters	Δρmin = −0.19 e Å^−3

Special details

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.

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

	x	y	z	Uiso*/Ueq
C1	0.36613 (18)	0.77456 (19)	0.59878 (16)	0.0284 (3)
C2	0.25933 (18)	0.6065 (2)	0.66526 (16)	0.0295 (3)
H2	0.1507	0.6289	0.5893	0.035*
C3	0.31028 (18)	0.4243 (2)	0.82842 (16)	0.0290 (3)
H3	0.4190	0.4066	0.9018	0.035*
C4	0.2111 (2)	0.2446 (2)	0.90640 (17)	0.0323 (3)
H4A	0.1414	0.2401	1.0450	0.039*
H4B	0.3320	0.0930	0.9135	0.039*
C5	0.0389 (2)	0.2791 (2)	0.78294 (19)	0.0372 (3)
H5A	−0.0864	0.4244	0.7812	0.056*
H5B	−0.0133	0.1517	0.8430	0.056*
H5C	0.1055	0.2834	0.6452	0.056*
O1	0.30172 (15)	0.93766 (15)	0.42861 (12)	0.0357 (3)
O2	0.50223 (14)	0.76619 (15)	0.69113 (12)	0.0361 (3)
H1	0.376 (3)	1.039 (4)	0.395 (3)	0.071 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0277 (5)	0.0275 (6)	0.0251 (5)	−0.0060 (4)	−0.0070 (4)	−0.0056 (4)
C2	0.0270 (5)	0.0326 (6)	0.0272 (5)	−0.0093 (5)	−0.0077 (4)	−0.0066 (4)
C3	0.0265 (5)	0.0325 (6)	0.0257 (5)	−0.0086 (4)	−0.0067 (4)	−0.0071 (4)
C4	0.0321 (6)	0.0332 (6)	0.0267 (5)	−0.0121 (5)	−0.0087 (4)	−0.0010 (4)
C5	0.0378 (6)	0.0382 (7)	0.0355 (6)	−0.0177 (5)	−0.0135 (5)	−0.0013 (5)
O1	0.0406 (5)	0.0339 (5)	0.0295 (4)	−0.0147 (4)	−0.0153 (3)	0.0015 (3)
O2	0.0402 (5)	0.0345 (5)	0.0332 (5)	−0.0155 (4)	−0.0166 (4)	−0.0005 (3)

Geometric parameters (Å, º)

C1—O2	1.2337 (14)	C4—C5	1.5239 (16)
C1—O1	1.3223 (13)	C4—H4A	0.9900
C1—C2	1.4723 (16)	C4—H4B	0.9900
C2—C3	1.3301 (16)	C5—H5A	0.9800
C2—H2	0.9500	C5—H5B	0.9800
C3—C4	1.4981 (16)	C5—H5C	0.9800
C3—H3	0.9500	O1—H1	0.95 (2)
O2—C1—O1	122.75 (11)	C5—C4—H4A	108.4
O2—C1—C2	123.99 (10)	C3—C4—H4B	108.4
O1—C1—C2	113.26 (10)	C5—C4—H4B	108.4
C3—C2—C1	122.03 (10)	H4A—C4—H4B	107.5
C3—C2—H2	119.0	C4—C5—H5A	109.5
C1—C2—H2	119.0	C4—C5—H5B	109.5
C2—C3—C4	125.63 (10)	H5A—C5—H5B	109.5
C2—C3—H3	117.2	C4—C5—H5C	109.5
C4—C3—H3	117.2	H5A—C5—H5C	109.5
C3—C4—C5	115.33 (10)	H5B—C5—H5C	109.5
C3—C4—H4A	108.4	C1—O1—H1	108.7 (12)
O2—C1—C2—C3	−3.05 (19)	C1—C2—C3—C4	−179.72 (10)
O1—C1—C2—C3	176.98 (11)	C2—C3—C4—C5	0.45 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2^i	0.95 (2)	1.69 (2)	2.6322 (13)	173.3 (19)

Symmetry code: (i) −x+1, −y+2, −z+1.