2,4,6-Trichloro­phenol

In the title compound, C₆H₃Cl₃O, the mol­ecular geometry approximates C_2v symmetry. The hydroxyl H atom lies in the plane of the ring; the closest approach between the centroids of aromatic rings of symmetry-related mol­ecules exceeds 3.8 Å.

Key indicators

• Single-crystal X-ray study
• T = 297 K
• Mean [sigma](C-C)= 0.004 Å
• R factor = 0.040
• wR factor = 0.109
• Data-to-parameter ratio = 15.7

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S1. Comment

The title molecule has been used in the past as an antiseptic, a pesticide for wood, leather and glue preservation, and also as an antimildew treatment for textiles. However, production was discontinued in the 1980 s and the molecule is no longer used in the USA, mainly because its production process systematically affords small quantities of dioxins and dibenzofurans. This molecule is currently listed as "reasonably anticipated to be a human carcinogen" (US Department of Health and Human Services, 2005). The corresponding phenolate has been used as a ligand for transition and non-transition metal ions, e.g. Cu^II (Gökaugaç et al., 1999), Mn^III (Wesolek et al., 1994), or Mg^II (Zechmann et al., 2000).

The molecular structure (Fig. 1) approximates a C_2v symmetry. However, the molecule is placed on a general position. The hydroxyl H atom lies in the plane of the aromatic ring and is oriented toward Cl6. The corresponding site oriented toward Cl2 is not available for hydroxyl H atom, as, due to crystal symmetry, it would give a short intermolecular H···H contact.

Interestingly, two polymorphs of pentafluorophenol have been reported (Das et al., 2006). For the Z' = 1 polymorph, hydroxyl H atom is placed 0.36 Å above the aromatic ring. A second polymorph, with Z' = 3, shows a variety of hydroxyl conformations. Two molecules are almost planar, with H deviations of 0.10 and 0.04 Å, while the third one has O—H bond almost normal to the aromatic ring, with the H atom placed 0.66 Å out of the benzene mean plane. In the same way, the title compound could present a degree of free rotation about the C—O bond, allowing the stabilization of polymorphic phases.

Regarding the crystal structure, no significant π···π interactions are observed. The closest approach between centroids of aromatic rings of symmetry-related molecules is 3.818 Å.

Related literature

For the carcinogenicity of the title molecule, see US Department of Health and Human Services (2005). For the polymorphism observed for a related molecule, pentafluorophenol, see Das et al. (2006). Metal-ion complexes including the phenolate ion of the title compound as ligand have been reported; see Gökaugaç et al. (1999); Wesolek et al. (1994); Zechmann et al. (2000).

S2. Experimental

A sample of the title compound was donated by the Chemistry Stores at Universidad Autónoma de Nuevo León (UANL), and used without previous recrystallization.

S3. Refinement

All H atoms were found in a difference map, but their positions regularized in order to get an idealized geometry for C—H and O—H groups. Constrained bond lengths: 0.82 (hydroxyl OH) and 0.93 Å (aromatic CH). Isotropic displacement parameters for H atoms were fixed to U_iso(H1) = 1.5 U_eq(O1); U_iso(H3) = 1.2 U_eq(C3); U_iso(H5) = 1.2 U_eq(C5).

Computing details

Data collection: XSCANS (Siemens, 1999); cell refinement: XSCANS (Siemens, 1999); data reduction: XSCANS (Siemens, 1999); program(s) used to solve structure: SHELXTL-Plus (Sheldrick, 1998); program(s) used to refine structure: SHELXTL-Plus (Sheldrick, 1998); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXTL-Plus (Sheldrick, 1998).

Figures

Fig. 1. The structure of the title molecule, with displacement ellipsoids at the 50% probability level for non-H atoms.

2,4,6-Trichlorophenol

Crystal data

C6H3Cl3O	F(000) = 392
Mr = 197.43	Dx = 1.806 Mg m^−3
Monoclinic, P21/c	Melting point: 342 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 3.8181 (18) Å	Cell parameters from 47 reflections
b = 15.742 (7) Å	θ = 6.0–12.4°
c = 12.127 (6) Å	µ = 1.18 mm^−1
β = 95.05 (4)°	T = 297 K
V = 726.1 (6) Å^3	Plate, colourless
Z = 4	0.60 × 0.20 × 0.04 mm

Data collection

Siemens P4 diffractometer	1086 reflections with I > 2σ(I)
Radiation source: medium-focus sealed tube, FN4	Rint = 0.089
Graphite monochromator	θmax = 26.0°, θmin = 2.1°
2θ/ω scans	h = −4→2
Absorption correction: gaussian (XSCANS; Siemens, 1999)	k = −19→1
Tmin = 0.792, Tmax = 0.954	l = −14→14
2445 measured reflections	3 standard reflections every 97 reflections
1427 independent reflections	intensity decay: 1.5%

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)] = 0.040	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.109	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0372P)^2 + 0.2366P] where P = (Fo^2 + 2Fc^2)/3
1427 reflections	(Δ/σ)max < 0.001
91 parameters	Δρmax = 0.28 e Å^−3
0 restraints	Δρmin = −0.38 e Å^−3

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

	x	y	z	Uiso*/Ueq
Cl2	1.2802 (2)	0.10705 (5)	0.52181 (6)	0.0599 (3)
Cl4	0.6704 (3)	0.06153 (5)	0.11139 (7)	0.0627 (3)
Cl6	0.7136 (2)	0.37081 (5)	0.29722 (6)	0.0587 (3)
O1	1.1072 (7)	0.28196 (14)	0.48426 (17)	0.0594 (6)
H1	1.0670	0.3331	0.4822	0.089*
C1	0.9955 (8)	0.23290 (17)	0.3971 (2)	0.0414 (6)
C2	1.0664 (7)	0.14727 (19)	0.4024 (2)	0.0420 (6)
C3	0.9675 (8)	0.09404 (17)	0.3154 (2)	0.0445 (6)
H3	1.0169	0.0362	0.3200	0.053*
C4	0.7952 (8)	0.12773 (17)	0.2219 (2)	0.0437 (6)
C5	0.7129 (7)	0.21246 (18)	0.2133 (2)	0.0413 (6)
H5	0.5911	0.2343	0.1498	0.050*
C6	0.8167 (8)	0.26403 (17)	0.3019 (2)	0.0408 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl2	0.0671 (5)	0.0637 (5)	0.0464 (4)	0.0052 (4)	−0.0082 (3)	0.0143 (3)
Cl4	0.0876 (6)	0.0460 (4)	0.0519 (4)	−0.0112 (4)	−0.0086 (4)	−0.0119 (3)
Cl6	0.0812 (6)	0.0372 (4)	0.0559 (5)	0.0080 (4)	−0.0031 (4)	−0.0018 (3)
O1	0.0813 (15)	0.0537 (12)	0.0406 (11)	0.0020 (11)	−0.0093 (10)	−0.0117 (9)
C1	0.0489 (16)	0.0407 (14)	0.0347 (12)	−0.0026 (13)	0.0049 (12)	−0.0037 (11)
C2	0.0429 (15)	0.0453 (14)	0.0374 (13)	0.0012 (12)	0.0023 (11)	0.0040 (11)
C3	0.0533 (17)	0.0355 (13)	0.0447 (15)	0.0015 (13)	0.0033 (13)	0.0034 (11)
C4	0.0529 (16)	0.0389 (14)	0.0396 (14)	−0.0059 (13)	0.0059 (12)	−0.0031 (11)
C5	0.0465 (16)	0.0427 (14)	0.0338 (13)	−0.0015 (12)	−0.0010 (11)	0.0009 (10)
C6	0.0466 (15)	0.0337 (13)	0.0419 (13)	0.0032 (12)	0.0032 (12)	0.0016 (11)

Geometric parameters (Å, º)

Cl2—C2	1.719 (3)	C2—C3	1.374 (4)
Cl4—C4	1.731 (3)	C3—C4	1.366 (4)
Cl6—C6	1.726 (3)	C3—H3	0.9300
O1—C1	1.347 (3)	C4—C5	1.372 (4)
O1—H1	0.8200	C5—C6	1.377 (4)
C1—C2	1.375 (4)	C5—H5	0.9300
C1—C6	1.379 (4)
C1—O1—H1	119.6	C3—C4—C5	122.1 (3)
O1—C1—C2	118.5 (3)	C3—C4—Cl4	119.2 (2)
O1—C1—C6	123.5 (3)	C5—C4—Cl4	118.7 (2)
C2—C1—C6	117.9 (2)	C4—C5—C6	117.7 (3)
C3—C2—C1	121.5 (3)	C4—C5—H5	121.1
C3—C2—Cl2	120.0 (2)	C6—C5—H5	121.1
C1—C2—Cl2	118.5 (2)	C5—C6—C1	122.1 (2)
C4—C3—C2	118.7 (3)	C5—C6—Cl6	120.0 (2)
C4—C3—H3	120.7	C1—C6—Cl6	117.9 (2)
C2—C3—H3	120.7
O1—C1—C2—C3	−178.4 (3)	C3—C4—C5—C6	1.4 (4)
C6—C1—C2—C3	0.9 (4)	Cl4—C4—C5—C6	−179.6 (2)
O1—C1—C2—Cl2	2.2 (4)	C4—C5—C6—C1	−0.4 (4)
C6—C1—C2—Cl2	−178.5 (2)	C4—C5—C6—Cl6	−178.7 (2)
C1—C2—C3—C4	0.0 (4)	O1—C1—C6—C5	178.5 (3)
Cl2—C2—C3—C4	179.4 (2)	C2—C1—C6—C5	−0.7 (4)
C2—C3—C4—C5	−1.2 (4)	O1—C1—C6—Cl6	−3.1 (4)
C2—C3—C4—Cl4	179.8 (2)	C2—C1—C6—Cl6	177.7 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···Cl6	0.82	2.58	2.960 (3)	110
O1—H1···Cl4^i	0.82	2.81	3.418 (3)	132

Symmetry code: (i) x, −y+1/2, z+1/2.