2,6-Difluoro­benzoic acid

Abstract

In the title compound, C₇H₄F₂O₂, the dihedral angle between the benzene ring and the carboxyl­ate group is 33.70 (14)°. In the crystal structure, inversion dimers linked by pairs of O—H⋯O hydro­gren bonds occur, generating R ₂ ²(8) loops. The dimers are linked into sheets lying parallel to (102) by C—H⋯F hydrogen bonds.

Related literature

For general background to 2,6-diflorobenzyl­chloride derivatives, see: Beavo (1995 ▶); Beavo & Reifsnyder (1990 ▶); Nicholson et al. (1991 ▶). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986 ▶).

Experimental

Crystal data

• C₇H₄F₂O₂

• M _r = 158.10

• Monoclinic,

• a = 3.6517 (4) Å

• b = 14.1214 (15) Å

• c = 12.2850 (13) Å

• β = 95.651 (3)°

• V = 630.42 (12) ų

• Z = 4

• Mo Kα radiation

• μ = 0.16 mm⁻¹

• T = 100 K

• 0.73 × 0.19 × 0.09 mm

Data collection

• Bruker APEXII DUO CCD diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2009 ▶) T _min = 0.841, T _max = 0.986

• 6112 measured reflections

• 2190 independent reflections

• 1895 reflections with I > 2σ(I)

• R _int = 0.029

Refinement

• R[F ² > 2σ(F ²)] = 0.049

• wR(F ²) = 0.143

• S = 1.12

• 2190 reflections

• 116 parameters

• All H-atom parameters refined

• Δρ_max = 0.47 e Å⁻³

• Δρ_min = −0.31 e Å⁻³

Data collection: APEX2 (Bruker, 2009 ▶); cell refinement: SAINT (Bruker, 2009 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 ▶).

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H1O2⋯O3i	0.95 (4)	1.68 (4)	2.6318 (14)	174 (4)
C3—H3⋯F2ii	0.98 (2)	2.54 (2)	3.3428 (16)	138.7 (16)

Symmetry codes: (i) ; (ii) .

supplementary crystallographic information

Comment

The derivatives of 2,6-diflorobenzylchloride involved in the inhibition of phosphodiesterases (PDEs) are enzymes which catalyze PDEs. These derivatives are classified into seven families, five of which, PDE1–PDE5, have been characterized (Beavo, 1995). The hydrolysis of cyclic nucleotides was evaluated according to the methods in given the references (Beavo & Reifsnyder, 1990; Nicholson et al., 1991).

The molecule of the title compound, (I), (Fig. 1) is not planar with the dihedral angle between the benzene ring and the carboxylate group being 33.70 (14)°. In the crystal structure, the molecules are linked into pairs of centrosymmetric dimers by intermolecular O2—H1O2···O3 hydrogren bonds (Table 1). These dimers are linked into two-dimensional plane by the intermolecular C3—H3A···F2 hydrogen bonds (Fig. 2, Table 1) parallel to (102).

Experimental

2,6-Difluorobenzylchloride (0.01 mol, 1.7 g) was added drop-wise with stirring into a round bottom flask containing 25 ml water and then refluxed for two and half hours. The gum compound precipitate formed was filtered and dissolved in alkaline water. Hydrochloric acid was then added drop-wise with stirring. The white precipitate formed was dissolved in methanol. Colourless needles of (I) were formed at room temperature overnight and filtrated and dried at 333 K.

Refinement

All hydrogen atoms were located in a difference Fourier map and refined freely.

Figures

Fig. 1.

The molecular structure of (I) with 50% probability ellipsoids for non-H atoms.

Fig. 2.

The crystal packing of (I), viewed down the b axis, showing two 2-D planes.

Crystal data

C7H4F2O2	F(000) = 320
Mr = 158.10	Dx = 1.666 Mg m−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3166 reflections
a = 3.6517 (4) Å	θ = 3.3–32.1°
b = 14.1214 (15) Å	µ = 0.16 mm−1
c = 12.2850 (13) Å	T = 100 K
β = 95.651 (3)°	Needle, colourless
V = 630.42 (12) Å3	0.73 × 0.19 × 0.09 mm
Z = 4

Data collection

Bruker APEXII DUO CCD diffractometer	2190 independent reflections
Radiation source: fine-focus sealed tube	1895 reflections with I > 2σ(I)
graphite	Rint = 0.029
φ and ω scans	θmax = 32.1°, θmin = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −5→5
Tmin = 0.841, Tmax = 0.986	k = −20→20
6112 measured reflections	l = −18→18

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.049	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.143	All H-atom parameters refined
S = 1.12	w = 1/[σ2(Fo2) + (0.0668P)2 + 0.3079P] where P = (Fo2 + 2Fc2)/3
2190 reflections	(Δ/σ)max < 0.001
116 parameters	Δρmax = 0.47 e Å−3
0 restraints	Δρmin = −0.31 e Å−3

Special details

Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.

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
F1	0.0410 (3)	−0.01635 (6)	0.16839 (7)	0.0312 (2)
F2	0.2348 (3)	0.26707 (6)	0.36896 (7)	0.0285 (2)
O2	0.2287 (3)	0.09843 (7)	0.46658 (7)	0.0238 (2)
O3	0.4751 (3)	−0.00746 (7)	0.35958 (8)	0.0222 (2)
C1	0.0163 (4)	0.07830 (9)	0.17659 (9)	0.0194 (2)
C2	−0.1413 (4)	0.12763 (10)	0.08679 (10)	0.0228 (3)
C3	−0.1734 (4)	0.22519 (10)	0.09441 (10)	0.0234 (3)
C4	−0.0482 (4)	0.27250 (10)	0.19005 (11)	0.0230 (3)
C5	0.1044 (4)	0.22003 (9)	0.27793 (9)	0.0184 (2)
C6	0.1398 (3)	0.12160 (8)	0.27576 (9)	0.0160 (2)
C7	0.2939 (3)	0.06665 (8)	0.37288 (9)	0.0156 (2)
H2	−0.221 (7)	0.0927 (16)	0.0182 (18)	0.038 (6)*
H3	−0.285 (6)	0.2599 (15)	0.0302 (17)	0.035 (5)*
H4	−0.074 (6)	0.3406 (16)	0.1979 (18)	0.035 (5)*
H1O2	0.341 (11)	0.062 (3)	0.526 (3)	0.098 (12)*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
F1	0.0518 (6)	0.0183 (4)	0.0219 (4)	0.0019 (4)	−0.0044 (4)	−0.0039 (3)
F2	0.0459 (6)	0.0169 (4)	0.0210 (4)	−0.0010 (4)	−0.0048 (4)	−0.0018 (3)
O2	0.0340 (6)	0.0238 (5)	0.0135 (4)	0.0038 (4)	0.0014 (4)	0.0013 (3)
O3	0.0269 (5)	0.0179 (4)	0.0216 (4)	0.0056 (4)	0.0012 (4)	0.0030 (3)
C1	0.0238 (6)	0.0181 (5)	0.0162 (5)	0.0001 (4)	0.0014 (4)	0.0003 (4)
C2	0.0242 (6)	0.0289 (6)	0.0150 (5)	−0.0002 (5)	−0.0006 (4)	0.0019 (4)
C3	0.0224 (6)	0.0289 (6)	0.0184 (5)	0.0037 (5)	−0.0001 (4)	0.0078 (4)
C4	0.0272 (6)	0.0193 (6)	0.0225 (6)	0.0041 (5)	0.0016 (5)	0.0062 (4)
C5	0.0210 (5)	0.0174 (5)	0.0166 (5)	0.0004 (4)	0.0012 (4)	0.0011 (4)
C6	0.0182 (5)	0.0160 (5)	0.0137 (4)	0.0009 (4)	0.0014 (4)	0.0019 (3)
C7	0.0174 (5)	0.0148 (5)	0.0148 (4)	−0.0006 (4)	0.0020 (4)	0.0012 (3)

Geometric parameters (Å, °)

F1—C1	1.3442 (15)	C2—H2	0.99 (2)
F2—C5	1.3467 (14)	C3—C4	1.3892 (19)
O2—C7	1.2794 (14)	C3—H3	0.98 (2)
O2—H1O2	0.96 (4)	C4—C5	1.3807 (17)
O3—C7	1.2574 (15)	C4—H4	0.97 (2)
C1—C2	1.3815 (17)	C5—C6	1.3965 (17)
C1—C6	1.3976 (16)	C6—C7	1.4866 (15)
C2—C3	1.387 (2)
C7—O2—H1O2	113 (2)	C5—C4—H4	119.3 (13)
F1—C1—C2	117.86 (11)	C3—C4—H4	122.2 (13)
F1—C1—C6	118.83 (11)	F2—C5—C4	117.84 (11)
C2—C1—C6	123.29 (12)	F2—C5—C6	118.74 (10)
C1—C2—C3	118.58 (12)	C4—C5—C6	123.38 (11)
C1—C2—H2	119.4 (13)	C5—C6—C1	115.44 (10)
C3—C2—H2	122.0 (13)	C5—C6—C7	122.18 (10)
C2—C3—C4	120.79 (11)	C1—C6—C7	122.37 (11)
C2—C3—H3	118.2 (13)	O3—C7—O2	123.76 (11)
C4—C3—H3	121.0 (13)	O3—C7—C6	119.51 (10)
C5—C4—C3	118.49 (12)	O2—C7—C6	116.72 (10)
F1—C1—C2—C3	179.13 (13)	C4—C5—C6—C7	−177.92 (12)
C6—C1—C2—C3	1.2 (2)	F1—C1—C6—C5	−179.87 (12)
C1—C2—C3—C4	0.3 (2)	C2—C1—C6—C5	−1.92 (19)
C2—C3—C4—C5	−0.9 (2)	F1—C1—C6—C7	−0.65 (19)
C3—C4—C5—F2	178.01 (12)	C2—C1—C6—C7	177.31 (12)
C3—C4—C5—C6	0.0 (2)	C5—C6—C7—O3	−147.25 (13)
F2—C5—C6—C1	−176.65 (11)	C1—C6—C7—O3	33.57 (18)
C4—C5—C6—C1	1.31 (19)	C5—C6—C7—O2	33.33 (17)
F2—C5—C6—C7	4.12 (18)	C1—C6—C7—O2	−145.84 (13)

Hydrogen-bond geometry (Å, °)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1O2···O3i	0.95 (4)	1.68 (4)	2.6318 (14)	174 (4)
C3—H3···F2ii	0.98 (2)	2.54 (2)	3.3428 (16)	138.7 (16)

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