4-Chloro-2,6-dinitro­phenol

The aromatic ring of the title compound, C₆H₃ClN₂O₅, is almost planar (r.m.s. deviation = 0.007 Å); one nitro substituent is nearly coplanar with the ring [dihedral angle = 3(1)°], whereas the other is twisted [dihedral angle = 36 (1)°]. The phenol OH group is intra­molecularly hydrogen bonded to the nitro group that is coplanar with the ring, generating an S(6) graph-set motif.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.007 Å
• R factor = 0.051
• wR factor = 0.098
• Data-to-parameter ratio = 10.9

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT230_ALERT_2_C Hirshfeld Test Diff for    Cl1    --  C1      ..       6.68 su
PLAT340_ALERT_3_C Low Bond Precision on  C-C Bonds (x 1000) Ang ..          7
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          3

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           25.00
           From the CIF: _reflns_number_total               1434
           Count of symmetry unique reflns          797
           Completeness (_total/calc)            179.92%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       637
           Fraction of Friedel pairs measured     0.799
           Are heavy atom types Z>Si present        yes
PLAT432_ALERT_2_G Short Inter X...Y Contact  O2     ..  C4      ..       3.01 Ang.
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          2
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K

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

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

S1. Comment

2,4,6-Trinitrophenol (picric acid) is a strong oxygen acid that dissociates in water. In the solid state, the molecule is nearly flat (Duesler et al., 1978; Soriano-Garcia et al., 1980). 4-Chloro-2,6-dinitrophenol (Scheme I) is also a similarly strong oxygen acid as it dissociates in water completely in water. In the crystal structure, the aromatic ring is nearly co-planar with one nitro substituent (dihedral angle 3(1) °) whereas it is twisted with respect to the other (dihedral angle 36 (1) °) (Fig. 1). The phenolic group is intra-molecularly hydrogen bonded to the nitro group that is co-planar with the ring.

Related literature

For the crystal structure of picric acid, see: Duesler et al. (1978); Soriano-Garcia et al. (1980).

S2. Experimental

Commercially available 4-chloro-2,6-dinitrophenol was recrystallized from methanol to yield colorless prisms.

S3. Refinement

Hydrogen atoms were placed in calculated positions (C–H 0.93 Å) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U_eq(C). The hydroxy H-atom was located in a difference Fourier map, and was refined with a distance restraint of O–H 0.84±0.01 Å.

Computing details

Data collection: RAPID-AUTO (Rigaku, 1998); cell refinement: RAPID-AUTO (Rigaku, 1998); data reduction: CrystalStructure (Rigaku/MSC, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

Fig. 1. Thermal ellipsoid plot (Barbour, 2001) of 4-chloro-2,6-dinitrophenol at the 50% probability level; hydrogen atoms are drawn as spheres of arbitrary radius.

4-Chloro-2,6-dinitrophenol

Crystal data

C6H3ClN2O5	F(000) = 220
Mr = 218.55	Dx = 1.761 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2yb	Cell parameters from 1662 reflections
a = 7.4700 (19) Å	θ = 4.1–27.4°
b = 5.8973 (15) Å	µ = 0.46 mm^−1
c = 9.952 (2) Å	T = 293 K
β = 109.939 (6)°	Prism, colorless
V = 412.13 (18) Å^3	0.24 × 0.21 × 0.18 mm
Z = 2

Data collection

Rigaku R-AXIS RAPID diffractometer	1434 independent reflections
Radiation source: fine-focus sealed tube	816 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.067
Detector resolution: 10.000 pixels mm^-1	θmax = 25.0°, θmin = 4.1°
ω scans	h = −8→8
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	k = −7→7
Tmin = 0.897, Tmax = 0.922	l = −11→11
3209 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.051	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.098	w = 1/[σ^2(Fo^2) + (0.0358P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max = 0.001
1434 reflections	Δρmax = 0.24 e Å^−3
131 parameters	Δρmin = −0.24 e Å^−3
2 restraints	Absolute structure: Flack (1983), 640 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.14 (14)

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

	x	y	z	Uiso*/Ueq
Cl1	0.4887 (2)	0.0000 (3)	0.86383 (14)	0.0688 (5)
O1	0.3354 (6)	0.5743 (6)	0.4395 (4)	0.0733 (13)
O2	0.2527 (5)	0.8807 (6)	0.5218 (4)	0.0721 (13)
O3	−0.0108 (6)	0.7765 (6)	0.6318 (4)	0.0604 (12)
H3	−0.101 (7)	0.774 (12)	0.664 (7)	0.10 (3)*
O4	−0.1986 (6)	0.6424 (8)	0.7898 (4)	0.0729 (14)
O5	−0.1056 (7)	0.3531 (8)	0.9292 (5)	0.0845 (14)
N1	0.2807 (6)	0.6773 (8)	0.5258 (5)	0.0497 (12)
N2	−0.0885 (7)	0.4861 (11)	0.8388 (5)	0.0594 (13)
C1	0.3379 (8)	0.2247 (7)	0.7937 (5)	0.0383 (13)
C2	0.3679 (7)	0.3605 (9)	0.6918 (6)	0.0430 (13)
H2	0.4672	0.3293	0.6582	0.052*
C3	0.2500 (6)	0.5442 (8)	0.6390 (5)	0.0376 (13)
C4	0.0974 (7)	0.5968 (8)	0.6866 (6)	0.0425 (13)
C5	0.0733 (7)	0.4491 (8)	0.7875 (5)	0.0387 (14)
C6	0.1891 (8)	0.2652 (9)	0.8411 (6)	0.0479 (15)
H6	0.1666	0.1703	0.9083	0.057*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0706 (9)	0.0606 (9)	0.0678 (10)	0.0225 (9)	0.0142 (8)	0.0110 (9)
O1	0.098 (3)	0.069 (3)	0.075 (3)	−0.012 (2)	0.058 (3)	0.002 (2)
O2	0.090 (3)	0.050 (3)	0.075 (3)	−0.002 (2)	0.027 (3)	0.018 (2)
O3	0.055 (3)	0.048 (2)	0.077 (3)	0.011 (2)	0.021 (3)	0.008 (2)
O4	0.063 (3)	0.083 (3)	0.084 (3)	0.023 (3)	0.038 (3)	0.001 (3)
O5	0.093 (3)	0.093 (3)	0.092 (4)	0.009 (3)	0.062 (3)	0.012 (3)
N1	0.052 (3)	0.055 (3)	0.043 (3)	−0.011 (2)	0.017 (3)	0.003 (3)
N2	0.062 (4)	0.065 (3)	0.057 (3)	−0.005 (3)	0.028 (3)	−0.019 (3)
C1	0.037 (3)	0.027 (3)	0.044 (3)	0.011 (2)	0.005 (3)	0.003 (2)
C2	0.039 (3)	0.047 (3)	0.044 (3)	0.000 (3)	0.016 (3)	−0.001 (3)
C3	0.034 (3)	0.042 (4)	0.034 (3)	−0.009 (3)	0.009 (2)	−0.002 (2)
C4	0.037 (3)	0.042 (3)	0.044 (3)	−0.001 (3)	0.007 (3)	−0.003 (3)
C5	0.037 (3)	0.041 (4)	0.040 (3)	−0.002 (3)	0.016 (3)	−0.005 (3)
C6	0.055 (4)	0.048 (3)	0.037 (3)	−0.004 (3)	0.012 (3)	−0.002 (3)

Geometric parameters (Å, º)

Cl1—C1	1.725 (4)	C1—C6	1.369 (7)
O1—N1	1.230 (5)	C1—C2	1.369 (6)
O2—N1	1.216 (5)	C2—C3	1.382 (7)
O3—C4	1.332 (6)	C2—H2	0.9300
O3—H3	0.84 (6)	C3—C4	1.410 (6)
O4—N2	1.221 (6)	C4—C5	1.387 (6)
O5—N2	1.233 (6)	C5—C6	1.376 (7)
N1—C3	1.454 (6)	C6—H6	0.9300
N2—C5	1.480 (6)
C4—O3—H3	107 (5)	C2—C3—C4	121.9 (5)
O2—N1—O1	124.0 (5)	C2—C3—N1	118.0 (4)
O2—N1—C3	119.2 (5)	C4—C3—N1	120.1 (5)
O1—N1—C3	116.9 (5)	O3—C4—C5	125.9 (5)
O4—N2—O5	123.3 (5)	O3—C4—C3	119.0 (5)
O4—N2—C5	119.5 (5)	C5—C4—C3	115.1 (4)
O5—N2—C5	117.3 (6)	C6—C5—C4	123.8 (4)
C6—C1—C2	120.7 (5)	C6—C5—N2	117.5 (5)
C6—C1—Cl1	119.3 (4)	C4—C5—N2	118.7 (5)
C2—C1—Cl1	120.0 (4)	C1—C6—C5	118.7 (5)
C1—C2—C3	119.7 (4)	C1—C6—H6	120.6
C1—C2—H2	120.1	C5—C6—H6	120.6
C3—C2—H2	120.1

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O4	0.84 (6)	1.82 (4)	2.563 (6)	146 (7)