Redetermination of trans-[beta]-hydro­muconic acid

The title compound (systematic name: trans-hex-3-enedioic acid), C₆H₈O₄, (I), is located on an inversion centre. A less accurate room-temperature structure has been reported previously [Ganis & Martuscelli (1966). Ric. Sci. 36, 439], without the position of the H atom involved in hydrogen bonding. The carboxylic acid groups of (I) link mol­ecules across inversion centres through O-H...O hydrogen-bonded pairs. The result of these inter­actions is the formation of chains with the graph-set description C₂²(18), which run along the c axis. The significance of this study lies in the analysis of the inter­actions occurring via hydrogen bonds, as well as in the comparison drawn between the mol­ecular structure of (I) and the structures of several other acid derivatives possessing two carboxylic acid groups.

S1. Comment

trans-Hex-3-enedioic acid, also known as trans-β-hydromuconic acid, is a human dicarboxylic acid metabolite of unsaturated fatty acids produced by the β-oxidation of trans-oct-3-enedioic acid (Jin & Tserng, 1989). The metabolic origin of trans-oct-3-enedioic acid is likely to be trans-9,10-octadecenoic acid, an unnatural fatty acid contained in partially hydrogenated oils. Thus, the title compound is a biologically important compound, which has attracted attention in relation to metabolic disorder of fatty acid oxidation in humans [e.g. dicarboxylic aciduria or unexplained attacks of lethargy and hypotonia, presumably related to episodes of fever and/or insufficient food intake (Tanaka & Hine, 1982; Tserng et al., 1990)] for which urinary excretions were reported to be increased. trans-Hex-3-enedioic acid is also of great importance for the synthesis of 3-alkylpyridine compounds, which are plausible biosynthetic precursors for the complex manzamine and related alkoloids (Baldwin et al., 2000). The title compound can be used as the starting material to prepare pent-4-enoic acid, which is formed by its pyrolysis (Shulman & Osteraas, 1963).

trans-β-Hydromuconic acid and adipic acid were the subjects of a study of the generation mechanism of the IR spectra of hydrogen-bonded molecular crystals (Flakus & Jabłońska, 2004; Flakus et al., 2006; Flakus & Hachuła, 2008; Hachuła, Nowak & Kusz, 2008; Hachuła, Pyzik, Nowak & Kusz, 2008). The IR spectra measurements of polycrystalline and monocrystalline samples of dicarboxylic acid derivatives, as well as theoretical analysis of the results, mainly focused on spectral effects corresponding to the intensity distribution, the influence of temperature, the linear dichroism and the isotopic substitution of deuterium in the above-mentioned molecules measured in the frequency range of the hydrogen and deuterium stretching vibration bands, ν_O–H and ν_O–D, respectively. The spectral studies were preceded by analysis of the crystal X-ray structure of the measured compounds. The crystal structure of adipic acid has been described previously (Housty & Hospital, 1965). The molecules of this compound form one-dimensional chains, with graph-set description C₂²(18), along the crystallographic c axis, in which the carboxyl groups are linked to each other via cyclic pairs of O—H···O bonds. The 295 K structure of (I) has already been reported (Ganis & Martuscelli, 1966) with an R factor of 12.0%. Thus, the precision of this structure determination was limited and additionally the position of the hydrogen-bonded H atom was not determined. In order to study interactions occurring via hydrogen bonds and molecular packing in this compound, we have now redetermined the structure of (I) using diffraction data collected at 298 K. Comparison of the unit-cell parameters of these structure determinations shows that there are no significant differences between them, and both the molecular packing and the crystal system remain unchanged. Ganis & Martuscelli (1966) described their structure in the standard space group P2₁/c, with a β angle of 134°. The matrix (101/010/-100) transforms their P2₁/c cell into a comparable P2₁/n cell with a = 7.90 Å, b = 4.67 Å, c = 9.40 Å and β = 105°, sufficiently close to the current values to be identical to the current unit cell. It can be mentioned that the present redetermination provides a much lower R value (3.58%) and the precision of the geometric parameters considerably increases [viz. σ(C—C) = 0.002 Å].

Compound (I) crystallizes with only one half-molecule in the asymmetric unit (Fig. 1). The molecule of (I) is in an extended conformation, so that atoms C2, C3, C3ⁱ and C2ⁱ are planar [symmetry code: (i) -x, -y, -z]. This planarity of the carbon chain is typical for even dicarboxylic acids (Thalladi et al., 2000). The single C—C bond lengths (Table 1) are similar to those in another saturated dicarboxylic acids possessing six C atoms (i.e. in adipic acid; C1—C2 = 1.487 Å and C2—C3 = 1.506 Å; Housty & Hospital, 1965). The ethylene bond length (C3═C3ⁱ) differs slightly from the values found in similar structures, fo example maleic acid (1.337 Å; James & Williams, 1974), α-fumaric acid (1.348 Å; Brown, 1966), β-fumaric acid (1.315 Å; Bednowitz & Post, 1966), and other unsaturated carboxylic acid derivatives such as acrylic acid [1.3285 (11) Å; Boese et al., 1999] or crotonic acid (1.293 Å; Shimizu et al., 1974). Moreover, this bond distancein (I) is considerably shorter than the value reported by Sutton (1965) for simple C═ C double bonds (1.335 Å).

The crystal structure of (I) differs slightly from those in other even, saturated and unsaturated, dicarboxylic acids, i.e. maleic acid (James & Williams, 1974), α-fumaric acid (Brown, 1966), β-fumaric acid (Bednowitz & Post, 1966), adipic acid (Housty & Hospital, 1965) and suberic acid (Gao et al., 1994). Firstly, the plane of the carboxyl group in (I) is twisted out of the plane of the chain zigzag (see the torsion angles given in Table 1). In some even diacids, the carboxyl groups are almost coplanar with the carbon chain, for example inβ-fumaric acid (O2—C1—C2—C3 = 179.26° and O1—C1—C2—C3 = 0.69°; Bednowitz & Post, 1966) or trans,trans-muconic acid (O2—C1—C2—C3 = 2.34° and O1—C1—C2—C3 = 177.96°; Bernstein & Leiserowitz, 1972). Secondly, the dihedral angle between the plane of the carbon chain and the plane of the carboxylic acid group O1/C1/O2 is 52.85 (20)°. By comparison, this angle is about 2.32° in maleic acid (James & Williams, 1974), 1.47° in α-fumaric acid (Brown, 1966), 1.36° in β-fumaric acid (Bednowitz & Post, 1966) and 0.51° in trans,trans-muconic acid (Bednowitz & Post, 1966). Similar values of this angle can be found in saturated dicarboxylic acids, for example 6.19° in adipic acid (Housty & Hospital, 1965), 6.43° in suberic acid (Gao et al., 1994) and 2.07° in sebacic acid (Bond et al., 2001). Thus, the twisting of the carboxyl group in (I) seems to cause the distortion of the molecule as a whole and introduces severe torsions into the carbon chains (Thalladi et al., 2000). The C–O and C═O bond distances in title compound are similar to those in other structures, for example, maleic acid (C1—O1 = 1.3 Å and C1—O2 = 1.222 Å; James & Williams, 1974), α-fumaric acid (C1—O1 = 1.287 Å and C1—O2 = 1.234 Å; Brown, 1966), β-fumaric acid (C1—O1 = 1.289 Å and C1—O2 = 1.228 Å; Bednowitz & Post, 1966) or trans,trans-muconic acid (C1—O1 = 1.297 Å and C1—O2 = 1.234 Å; Bernstein & Leiserowitz, 1972). Thus, these C–O and C═O bond distances in (I) are in normal ranges and are also comparable to the mean values given by Allen et al. (1987) for a variety carboxyl groups (C—OH = 1.308 Å and C═O = 1.214 Å). The bond-angle values at the central C atom in the carboxyl group also agree with the mean values specified by Borthwick (1980) for a typical carboxylic acid group [O2—C1—C2 = 123 (2) Å and O1—C1–C2 = 112 (2) Å].

The molecules of (I) lie on inversion centres with an all-trans conformation. Each of these molecules has two terminal groups (carboxyl groups), which link them across an inversion centre through two O—H···O hydrogen bonds. Atom O1 of the hydroxy OH group in the molecule at (x, y, z) acts as a hydrogen-bond donor, via H1, to carbonyl atom O2 belonging to the molecule at (-x, -y, -z + 1), and in turn, carbonyl atom O2 in the molecule at (x, y, z) is an acceptor in a hydrogen bond to the hydroxy OH group of the molecule at (-x, -y, -z + 1) (Fig. 2 and Table 2). These interactions lead to the formation of cyclic dimers with a graph-set motif of R₂²(8) (Etter et al., 1990; Bernstein et al., 1995; Motherwell et al., 1999). The carboxy dimer motifs connect lateral molecules in an end-to-end manner to generate infinite hydrogen-bonded chains [graph-set C₂²(18)] that run along the c axis. The same graph-set motif of C₂²(18) is found in most, saturated as well as unsaturated, dicarboxylic acids with some exceptions (such as the α form of oxalic acid or some 1,2-disubstituted acids). The molecules of the α form of oxalic acid are connected through O—H···O hydrogen bonds forming a catemer motif (Derissen & Smith, 1974). 1,2-Disubstituted acids, such as maleic acid or furan-3,4-dicarboxylic acid, are linked by both intra- and intermolecular hydrogen bonds, resulting in infinite chains (Leiserowitz, 1976).

The polycrystalline spectru of trans-β-hydromuconic acid is shown in Fig. 3. From the values of the H—O and O···O distances, as well the O—H···O angle, recorded in Table 2 it can be noticed that the hydrogen bond in (I) is of medium strength (Desiraju & Steiner, 1999; Steiner, 2002). In addition, the ν_O–H stretching vibration band of the title compound covers a broad frequency range of 3500–2100 cm^-1, and the polycrystalline OH band is shifted towards the lower frequencies by ca 620 cm^-1 in relation to the unperturbed value of 3570 cm^-1. This shift in the OH stretch frequency proves that the O—H···O hydrogen bond is a medium strong. A familiar correlation between the hydrogen-bond energy and the frequency shift of the hydrogen (or deuteron) stretching vibration band is used to justify this statement (Schuster et al., 1976; Schuster & Mikenda, 1999). Judging from the bond lengths, the O—H···O hydrogen bond between two trans-β-hydromuconic acid molecules [O1···O2 = 2.6680 (16) Å] appears to be slightly weaker than the hydrogen bond involving two adipic acid molecules (O1···O2 = 2.642 Å). However, this O—H···O bond is stronger than those in α-fumaric acid (O1···O2 = 2.684 Å) or β-fumaric acid (O1···O2 = 2.673 Å). Consequently, the stronger O—H···O hydrogen bonds correspond to a larger frequency shift. It can also be noted that the O—H bond length in the title compound is comparable to the mean value reported by Allen et al. (1987) for the hydroxy group in carboxylic acid systems (O—H = 1.015 Å).

Related literature

For related literature, see: Allen et al. (1987); Baldwin et al. (2000); Bednowitz & Post (1966); Bernstein & Leiserowitz (1972); Bernstein et al. (1995); Boese et al. (1999); Bond et al. (2001); Borthwick (1980); Brown (1966); Derissen & Smith (1974); Desiraju & Steiner (1999); Etter et al. (1990); Flakus & Hachuła (2008); Flakus & Jabłońska (2004); Flakus et al. (2006); Ganis & Martuscelli (1966); Gao et al. (1994); Hachuła et al. (2008a, 2008b); Housty & Hospital (1965); James & Williams (1974); Jin & Tserng (1989); Leiserowitz (1976); Motherwell et al. (1999); Schuster & Mikenda (1999); Schuster et al. (1976); Shimizu et al. (1974); Shulman & Osteraas (1963); Steiner (2002); Sutton (1965); Tanaka & Hine (1982); Thalladi et al. (2000); Tserng et al. (1990).

S2. Experimental

trans-β-Hydromuconic acid (98% pure) was purchased from Sigma–Aldrich. Slow crystallization from an acetone solution, over a period of several days at room temperature, afforded single crystals of (I) suitable for X-ray diffraction.

S3. Refinement

H atoms that take part in hydrogen bonding were located in a difference Fourier map and refined freely with isotropic displacement parameters. Other H atoms were introduced in geometrically idealized positions and refined with an appropriate riding model, with C—H distances of 0.99 Å (CH₂) and 0.96 Å (CH); their U_iso(H) values were set at 1.2U_eq(C).

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2008).

Figures

	Fig. 1. The asymmetric unit of (I), with the atom-numbering scheme, showing 50% probability displacement ellipsoids. H atoms are shown as small spheres of arbitrary radius. [Symmetry codes: (i) -x, -y, -z.]
	Fig. 2. Part of the crystal structure of (I), viewed along the b axis, showing the R2^2(8) rings. Atoms marked with an asterisk (*) are at the symmetry position (-x, -y, -z + 1). The dashed lines indicate the hydrogen-bonding interactions. For the sake of clarity, all H atoms bonded to C atoms have bee omitted.
	Fig. 3. The IR spectrum of the trans-β-hydromuconic acid sample dispersed in a KBr pellet.

trans-hex-3-enedioic acid

Crystal data

C6H8O4	F(000) = 152
Mr = 144.12	Dx = 1.442 Mg m^−3
Monoclinic, P21/n	Melting point = 468–469 K
Hall symbol: -P 2yn	Mo Kα radiation, λ = 0.71073 Å
a = 7.781 (2) Å	Cell parameters from 1001 reflections
b = 4.665 (1) Å	θ = 2.3–32.7°
c = 9.516 (2) Å	µ = 0.12 mm^−1
β = 106.01 (3)°	T = 298 K
V = 332.01 (13) Å^3	Block, colourless
Z = 2	0.28 × 0.14 × 0.08 mm

Data collection

Oxford Diffraction KM-4 diffractometer with a Sapphire3 CCD detector	441 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.015
Graphite monochromator	θmax = 25.0°, θmin = 3.0°
Detector resolution: 16.0328 pixels mm^-1	h = −9→9
ω scans	k = −2→5
1971 measured reflections	l = −10→11
582 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)] = 0.036	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.108	H atoms treated by a mixture of independent and constrained refinement
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0781P)^2] where P = (Fo^2 + 2Fc^2)/3
582 reflections	(Δ/σ)max < 0.001
50 parameters	Δρmax = 0.13 e Å^−3
0 restraints	Δρmin = −0.19 e Å^−3

Special details

Experimental. The IR spectrum of polycrystalline sample of trans-β-hydromuconic acid dispersed in KBr was measured at the temperature of liquid nitrogen using an FT—IR Nicolet Magna 560 spectrometer operating at resolution of 2 cm-1. The IR spectrum was recorded in the range 1000–4000 cm-1 using a Ever-Glo source, a KBr beamsplitter and a DTGS detector.

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
O1	−0.11364 (17)	−0.2780 (3)	0.37552 (12)	0.0595 (5)
O2	0.07307 (18)	0.0674 (3)	0.35662 (12)	0.0611 (5)
C1	−0.0212 (2)	−0.1339 (3)	0.30437 (16)	0.0415 (5)
C2	−0.0421 (2)	−0.2406 (3)	0.15266 (15)	0.0488 (5)
H2A	0.0099	−0.4306	0.1581	0.059*
H2B	−0.1687	−0.2580	0.1034	0.059*
C3	0.0417 (2)	−0.0552 (3)	0.06327 (16)	0.0421 (5)
H3	0.1629	−0.0146	0.1002	0.050*
H1O	−0.089 (3)	−0.196 (4)	0.478 (3)	0.098 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0887 (11)	0.0599 (8)	0.0372 (7)	−0.0185 (7)	0.0294 (7)	−0.0047 (6)
O2	0.0806 (10)	0.0705 (9)	0.0374 (7)	−0.0241 (7)	0.0248 (7)	−0.0112 (6)
C1	0.0539 (10)	0.0386 (8)	0.0343 (9)	0.0033 (8)	0.0162 (8)	0.0024 (7)
C2	0.0746 (13)	0.0422 (9)	0.0329 (10)	−0.0017 (8)	0.0202 (9)	−0.0031 (6)
C3	0.0499 (10)	0.0473 (9)	0.0311 (8)	0.0014 (7)	0.0149 (7)	−0.0058 (6)

Geometric parameters (Å, º)

O1—C1	1.3022 (18)	C2—H2A	0.9700
O1—H1O	1.02 (2)	C2—H2B	0.9700
O2—C1	1.2109 (19)	C3—C3^i	1.306 (3)
C1—C2	1.493 (2)	C3—H3	0.9300
C2—C3	1.484 (2)
C1—O1—H1O	108.8 (13)	C3—C2—H2B	108.7
O2—C1—O1	123.08 (14)	C1—C2—H2B	108.7
O2—C1—C2	123.20 (14)	H2A—C2—H2B	107.6
O1—C1—C2	113.72 (14)	C3^i—C3—C2	124.9 (2)
C3—C2—C1	114.34 (13)	C3^i—C3—H3	117.5
C3—C2—H2A	108.7	C2—C3—H3	117.5
C1—C2—H2A	108.7
O2—C1—C2—C3	−8.2 (2)	C1—C2—C3—C3^i	−124.0 (2)
O1—C1—C2—C3	171.94 (14)

Symmetry code: (i) −x, −y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···O2^ii	1.02 (2)	1.66 (2)	2.6680 (16)	174 (2)

Symmetry code: (ii) −x, −y, −z+1.