(4-Hydroxy­phen­oxy)acetic acid

The carboxyl groups in mol­ecules of the title compound, C₈H₈O₄, are held together by R₂²(8) hydrogen bonding. The -OH groups at postion 4 on the aryl rings are linked by continuous hydrogen-bonded chains. The supra­molecular structure is further defined by the formation of R₆⁶(44) rings.

Key indicators

• Single-crystal X-ray study
• T = 120 K
• Mean [sigma](C-C) = 0.001 Å
• R factor = 0.034
• wR factor = 0.099
• Data-to-parameter ratio = 14.9

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT180_ALERT_3_C Check Cell Rounding: # of Values Ending with 0 =          3

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

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
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S1. Comment

4-hydroxyphenoxyacetic acid has been found in phenoxymethyl penicillin fermentations (Birner, 1972) and its molecular structure was determined to establish the hydrogen bonding patterns in the crystal. Apart from the methylene H atoms the molecule is essentially planar and the torsion angle with the greatest deviation from zero or ±180° is C7—O2—C1—C2 = 6.62 (14)°. The molecular structure is shown in Figure 1, a partial packing diagram is given in Figure 2 and selected geometric parameters are listed in Table 1. Details of the hydrogen bonding are shown in Table 2.

As is often the case for monocarboxylic acids the carboxylate groups are linked by intermolecular hydrogen bonding to form a R²₂(8) ring across a centre of symmetry. Weaker hydrogen bonding is also present between the 4-hydroxy groups that link an infinite chain of molecules. Taken in combination the two hydrogen motifs also form R⁶₆(44) rings involving four molecules.

Other interactions involve a C5—H5···O3 contact and one C—H···π bonding distance (Table 2) less than 3 Å (where Cg is the centre of the aryl ring).

Related structures include phenylacetic acid (Hodgson & Asplund, 1991), 4-methoxyphenoxyacetic acid (Kumar & Rao, 1982) and 2-methylphenoxyacetic acid (Cox & Hickey, 2004).

Related literature

For related literature, see: Birner (1972); Cox & Hickey (2004); Hodgson & Asplund (1991); Kumar & Rao (1982).

S2. Experimental

The sample was purchased from Aldrich and was recrystallized from ethanol.

S3. Refinement

All non-hydrogen atoms were refined by full-matrix least squares calculations with anisotropic displacement parameters. All the hydrogen atoms were allowed to ride on their attached atoms with isotropic displacement parameters 1.2 times those of the U_eq of their attached atoms. The constrained C—H distances were 0.95 Å (aromatic), 0.99 Å (methylene) and 0.84 Å (hydroxy).

Computing details

Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Nonius, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. View of (I) (50% probability displacement ellipsoids)
	Fig. 2. A partial packing diagram of (I) showing R^22(8) and R^66(44) ring formations. Symbols used to denote symmetry positions of atom coordinates are: asterisk (*) = 2 - x, -y, -z; dollar ($) = -x, 1/2 + y, 0.5 - z and hash (#) = -x, -1/2 + y, 0.5 - z.

(4-Hydroxyphenoxy)acetic acid

Crystal data

C8H8O4	F(000) = 352
Mr = 168.14	Dx = 1.531 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1796 reflections
a = 8.6550 (2) Å	θ = 2.9–27.5°
b = 5.2531 (1) Å	µ = 0.12 mm^−1
c = 16.2401 (4) Å	T = 120 K
β = 98.983 (1)°	Block, colourless
V = 729.31 (3) Å^3	0.6 × 0.45 × 0.38 mm
Z = 4

Data collection

Bruker Nonius KappaCCD area-detector diffractometer	1518 reflections with I > 2σ(I)
φ and ω scans to fill Ewald sphere	Rint = 0.022
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	θmax = 27.5°, θmin = 3.2°
Tmin = 0.844, Tmax = 0.954	h = −10→11
9200 measured reflections	k = −5→6
1666 independent reflections	l = −20→18

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.034	w = 1/[σ^2(Fo^2) + (0.0599P)^2 + 0.1898P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.099	(Δ/σ)max < 0.001
S = 1.07	Δρmax = 0.35 e Å^−3
1666 reflections	Δρmin = −0.23 e Å^−3
112 parameters

Special details

Experimental. Please note cell_measurement_ fields are not relevant to area detector data, the entire data set is used to refine the cell, which is indexed from all observed reflections in a 10 degree phi range.

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
O1	0.03717 (8)	0.18406 (14)	0.22174 (5)	0.0183 (2)
H1	0.0231	0.0486	0.247	0.022*
O2	0.58461 (8)	0.16604 (13)	0.08499 (4)	0.0169 (2)
O3	0.92145 (8)	−0.20002 (14)	0.07019 (5)	0.0184 (2)
H31	0.9935	−0.1832	0.0414	0.022*
O4	0.84072 (8)	0.17346 (14)	0.01142 (4)	0.0188 (2)
C1	0.45139 (11)	0.15605 (18)	0.12213 (6)	0.0132 (2)
C2	0.42258 (11)	−0.03065 (19)	0.17835 (6)	0.0150 (2)
H2	0.4964	−0.163	0.1934	0.018*
C3	0.28426 (11)	−0.02249 (19)	0.21258 (6)	0.0152 (2)
H3	0.2645	−0.1483	0.2516	0.018*
C4	0.17624 (11)	0.16823 (18)	0.18973 (6)	0.0139 (2)
C5	0.20589 (11)	0.35600 (19)	0.13400 (6)	0.0158 (2)
H5	0.1319	0.4881	0.119	0.019*
C6	0.34355 (12)	0.35056 (18)	0.10027 (6)	0.0152 (2)
H6	0.3642	0.4793	0.0624	0.018*
C7	0.68607 (11)	−0.04464 (19)	0.10067 (6)	0.0153 (2)
H7A	0.6296	−0.2028	0.0813	0.018*
H7B	0.7228	−0.0601	0.1613	0.018*
C8	0.82384 (11)	−0.00948 (19)	0.05559 (6)	0.0145 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0148 (4)	0.0192 (4)	0.0228 (4)	0.0023 (3)	0.0094 (3)	0.0016 (3)
O2	0.0130 (4)	0.0179 (4)	0.0213 (4)	0.0040 (3)	0.0076 (3)	0.0050 (3)
O3	0.0150 (4)	0.0204 (4)	0.0212 (4)	0.0059 (3)	0.0071 (3)	0.0051 (3)
O4	0.0168 (4)	0.0185 (4)	0.0223 (4)	0.0031 (3)	0.0069 (3)	0.0047 (3)
C1	0.0108 (5)	0.0154 (5)	0.0138 (4)	−0.0012 (3)	0.0029 (3)	−0.0022 (3)
C2	0.0134 (5)	0.0146 (5)	0.0171 (5)	0.0019 (3)	0.0023 (3)	0.0008 (3)
C3	0.0156 (5)	0.0151 (5)	0.0157 (4)	−0.0008 (3)	0.0044 (4)	0.0017 (3)
C4	0.0113 (4)	0.0163 (5)	0.0147 (4)	−0.0010 (3)	0.0034 (3)	−0.0030 (3)
C5	0.0146 (5)	0.0152 (5)	0.0177 (5)	0.0032 (3)	0.0028 (4)	0.0004 (3)
C6	0.0162 (5)	0.0141 (5)	0.0156 (4)	0.0004 (3)	0.0032 (4)	0.0015 (3)
C7	0.0127 (4)	0.0167 (5)	0.0173 (5)	0.0026 (4)	0.0042 (3)	0.0023 (4)
C8	0.0126 (4)	0.0173 (5)	0.0136 (4)	0.0004 (3)	0.0020 (3)	−0.0013 (3)

Geometric parameters (Å, º)

O1—C4	1.3861 (11)	C2—H2	0.95
O1—H1	0.84	C3—C4	1.3810 (14)
O2—C1	1.3832 (11)	C3—H3	0.95
O2—C7	1.4110 (12)	C4—C5	1.3894 (14)
O3—C8	1.3074 (12)	C5—C6	1.3871 (13)
O3—H31	0.84	C5—H5	0.95
O4—C8	1.2215 (12)	C6—H6	0.95
C1—C2	1.3887 (14)	C7—C8	1.5048 (13)
C1—C6	1.3920 (14)	C7—H7A	0.99
C2—C3	1.3971 (13)	C7—H7B	0.99
C4—O1—H1	109.5	C6—C5—C4	120.00 (9)
C1—O2—C7	115.42 (7)	C6—C5—H5	120
C8—O3—H31	109.5	C4—C5—H5	120
O2—C1—C2	124.12 (9)	C5—C6—C1	119.83 (9)
O2—C1—C6	115.61 (8)	C5—C6—H6	120.1
C2—C1—C6	120.27 (9)	C1—C6—H6	120.1
C1—C2—C3	119.53 (9)	O2—C7—C8	109.51 (8)
C1—C2—H2	120.2	O2—C7—H7A	109.8
C3—C2—H2	120.2	C8—C7—H7A	109.8
C4—C3—C2	120.10 (9)	O2—C7—H7B	109.8
C4—C3—H3	119.9	C8—C7—H7B	109.8
C2—C3—H3	119.9	H7A—C7—H7B	108.2
C3—C4—O1	122.26 (9)	O4—C8—O3	125.14 (9)
C3—C4—C5	120.26 (9)	O4—C8—C7	123.97 (9)
O1—C4—C5	117.47 (8)	O3—C8—C7	110.89 (8)
C7—O2—C1—C2	6.62 (14)	O1—C4—C5—C6	179.69 (8)
C7—O2—C1—C6	−173.88 (8)	C4—C5—C6—C1	0.27 (15)
O2—C1—C2—C3	179.73 (8)	O2—C1—C6—C5	179.67 (8)
C6—C1—C2—C3	0.25 (14)	C2—C1—C6—C5	−0.81 (15)
C1—C2—C3—C4	0.84 (14)	C1—O2—C7—C8	179.19 (7)
C2—C3—C4—O1	179.81 (8)	O2—C7—C8—O4	−1.16 (13)
C2—C3—C4—C5	−1.38 (15)	O2—C7—C8—O3	178.87 (8)
C3—C4—C5—C6	0.82 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O1^i	0.84	2.07	2.8878 (6)	165
O3—H31···O4^ii	0.84	1.78	2.6201 (10)	173
C5—H5···O3^iii	0.95	2.49	3.4318 (12)	174
C2—H2···Cg^iv	0.95	2.87	3.6190 (11)	136

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