2-All­yloxy-5-chloro­benzoic acid

The title compound, C₁₀H₉ClO₃, is an ether derived from salicylic acid. The asymmetric unit contains one independent mol­ecule that is linked through centrosymmetrically related O—H...O hydrogen bonds by carboxyl pairing. The compound was prepared as a model for the analysis of the influence of electrostatic stabilization and intra­molecular hydrogen bonding in [3,3]-sigmatropic Claisen reactions, such as the chorismate-to-prephenate rearrangement, catalyzed by chorismate mutase.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.044
• wR factor = 0.125
• Data-to-parameter ratio = 13.6

checkCIF/PLATON results

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Alert level C
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C7

Alert level G
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
   1 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

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

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S1. Comment

The intramolecular Claisen rearrangement of chorismate to prephenate, catalyzed by chorismate mutase, represents a rare case of a [3,3] sigmatropic shift reaction in live organisms and corresponds to a key step in the pathway to form aromatic amino acids in plants, bacteria and fungi (Ziegler, 1977; Castro, 2004; Zhang et al., 2005). This unimolecular reaction occurs at the active site of the enzyme without formation of an enzyme-substrate covalent intermediate and it has been proposed that the transition state structures in the gas phase, water and enzyme are characteristic of a concerted pericyclic rearrangement. Since we are interested in the systematic analysis of the influence of electrostatic stabilization and intramolecular hydrogen bonding in [3,3] sigmatropic Claisen rearrangements, a series of ethers derived from salicylic acid has been synthesized. The 2-allyloxy-5-chlorobenzoic acid (I) is a new synthesized compound and here we report its X-ray crystal structure.

A projection of the crystal structure and the numbering of the non-hydrogen atoms are shown in Fig. 1 and the selected bond lengths and angles are given in Table 1. The data in Table 1 show that in the aromatic ring the C3—C4, C4—C5 and C5—C6 bonds are the strongest (shortest) C≐C ring bonds, probably as a consequence of electronic effects and the strain induced by ortho-substitution at C1 and C2. The carboxyl and ether groups are planar, but they are not perfectly coplanar with the aromatic ring plane and deviate by 8.1 (3)° for carboxyl and by 15.0 (2)° for ether. The electron withdrawing influence of the carboxyl group weakens the C1—C2 and C2—C3 bonds which made them longer than the other ring bonds. These effects are similar to those found in p-chlorobenzoic acid (II) (Colapietro & Domenicano, 1982). The Cl atom in (I) has a small effect on the C3—C4—C5 angle [120.4 (2)°], but the COOH group reduces the C1—C2—C3 angle from 120° (normal benzene ring) to 119.37 (19)°. The effect is opposite to that found in compound (II), where the C3—C4—C5 angle is 122.0° and C1—C2—C3 angle is 120.1°. This evidently results from the presence of the allyloxy group in (I), lengthening both C1—C2 and C1—C6 bonds, and reducing the C2—C1—C6 angle to 118.9 (2)°. Closely similar effects are observed for 2-methoxymethoxybenzoic acid, where the ortho-substituent is electronically and sterically similar (Jones et al., 1984).

A pair of molecules of (I) is connected through the carboxyl groups by centrosymmetric hydrogen bonds (O1—H1···O2ⁱ, O1···O2ⁱ 2.636 (2) Å, < (O1—H1^···O2ⁱ) 167.2°, symmetry code is: -x, -y, -z), which are stacked into sheets along a axis (Fig. 2). There is some interaction between O2 and O3 atoms with 2.622 (2) Å distance, a distance which - though short - is fairly normal for systems like this with the plane of the COOH group close to coplanar with the ring and is probably a consequence of the crystal-packing forces.

Related literature

For related literature, see: Castro (2004); Colapietro & Domenicano (1982); Jones et al. (1984); White et al. (1958); Zhang et al. (2005); Ziegler (1977).

S2. Experimental

Preparation of 2-allyloxy-5-chlorobenzoic Acid followed closely the procedure of White et al. (1958). A mixture of 8.63 g (50 mmol) of 5-chlorosalycilic acid, 6.05 g (0.05 mole) of allyl bromide, 8.29 g (60 mmol) of dry, powdered potassium carbonate, and sufficient dry acetone (about 30 ml) to give an easily stirred mass was stirred and refluxed for eight hours. Then the mixture was filtered, acidified with diluted acetic acid and the acetone removed by distillation under reduced pressure. The residue was initially purified by crystallization from acetone water (m.p. 75–76°C). Colorless crystals of (I) were grown from aqueous solution by slow evaporation at room temperature.

S3. Refinement

All non-H atoms were refined with anisotropic displacement parameters. H atom of the carboxylic moiety was found from Fourier map. This H atom was treated with riding model and they U_eq fixed at 1.2 times of the parent atom. H atoms bonded to C atoms were added at their calculated positions and included in the structure factor caculations, with C—H distances and U_eq taken from default of the refinement program.

Computing details

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: SET4 in CAD-4 EXPRESS; data reduction: HELENA (Spek, 1996); 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) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Molecular structure of (I) with labeling scheme. Ellipsoids at 40% probability level.
	Fig. 2. Packing of (I) showing the pair of molecules connected through hydrogen bonds and stacked along a axis.
	Fig. 3. Schematic representations of the structures of (I) and (II).

2-Allyloxy-5-chlorobenzoic acid

Crystal data

C10H9ClO3	F(000) = 440
Mr = 212.62	Dx = 1.448 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71069 Å
a = 8.800 (1) Å	Cell parameters from 25 reflections
b = 15.201 (2) Å	θ = 5.6–17.1°
c = 7.372 (1) Å	µ = 0.37 mm^−1
β = 98.469 (3)°	T = 293 K
V = 975.4 (2) Å^3	Irregular block, colourless
Z = 4	0.47 × 0.26 × 0.16 mm

Data collection

Enraf–Nonius CAD-4 diffractometer	Rint = 0.018
Radiation source: fine-focus sealed tube	θmax = 25.1°, θmin = 2.3°
Graphite monochromator	h = −10→0
ω/2θ scans	k = 0→18
1848 measured reflections	l = −8→8
1732 independent reflections	3 standard reflections every 200 reflections
1405 reflections with I > 2σ(I)	intensity decay: 1%

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)] = 0.044	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.125	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0689P)^2 + 0.372P] where P = (Fo^2 + 2Fc^2)/3
1732 reflections	(Δ/σ)max < 0.001
127 parameters	Δρmax = 0.40 e Å^−3
0 restraints	Δρmin = −0.29 e Å^−3

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

	x	y	z	Uiso*/Ueq
C1	0.0102 (3)	0.14496 (14)	0.5102 (3)	0.0390 (5)
C2	0.1059 (2)	0.09010 (13)	0.4234 (3)	0.0368 (5)
C3	0.2527 (3)	0.07040 (14)	0.5121 (3)	0.0400 (5)
H3	0.3161	0.0334	0.4562	0.048*
C4	0.3046 (3)	0.10546 (15)	0.6823 (3)	0.0426 (5)
C5	0.2134 (3)	0.16168 (16)	0.7646 (3)	0.0522 (6)
H5	0.2504	0.1864	0.8779	0.063*
C6	0.0676 (3)	0.18149 (16)	0.6798 (3)	0.0500 (6)
H6	0.0066	0.2197	0.7363	0.060*
C7	0.0576 (2)	0.05211 (14)	0.2379 (3)	0.0386 (5)
O1	0.1500 (2)	−0.00428 (13)	0.1857 (2)	0.0702 (6)
H1	0.1171	−0.0215	0.0586	0.084*
O2	−0.0616 (2)	0.07367 (13)	0.1405 (2)	0.0694 (6)
O3	−0.13381 (18)	0.15949 (11)	0.4243 (2)	0.0472 (4)
C8	−0.2398 (3)	0.20355 (17)	0.5228 (3)	0.0486 (6)
H8A	−0.2133	0.2654	0.5364	0.058*
H8B	−0.2356	0.1781	0.6441	0.058*
C9	−0.3964 (3)	0.19380 (16)	0.4193 (3)	0.0495 (6)
H9	−0.4751	0.2238	0.4642	0.059*
C10	−0.4343 (3)	0.14708 (17)	0.2713 (3)	0.0551 (6)
H10A	−0.3595	0.1159	0.2214	0.066*
H10B	−0.5362	0.1449	0.2157	0.066*
Cl1	0.48749 (7)	0.07853 (4)	0.79134 (8)	0.0581 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0422 (11)	0.0380 (11)	0.0363 (11)	−0.0039 (9)	0.0043 (9)	−0.0040 (8)
C2	0.0446 (12)	0.0340 (10)	0.0312 (10)	−0.0033 (9)	0.0035 (9)	−0.0022 (8)
C3	0.0463 (13)	0.0368 (11)	0.0365 (11)	−0.0008 (9)	0.0043 (9)	−0.0032 (9)
C4	0.0484 (12)	0.0425 (12)	0.0344 (11)	−0.0052 (9)	−0.0022 (9)	−0.0002 (9)
C5	0.0588 (15)	0.0575 (15)	0.0374 (12)	−0.0080 (11)	−0.0021 (11)	−0.0139 (11)
C6	0.0525 (14)	0.0524 (14)	0.0449 (13)	−0.0009 (11)	0.0065 (11)	−0.0196 (11)
C7	0.0421 (12)	0.0396 (11)	0.0334 (11)	0.0025 (9)	0.0028 (9)	−0.0051 (9)
O1	0.0670 (12)	0.0902 (14)	0.0474 (10)	0.0327 (10)	−0.0119 (9)	−0.0334 (9)
O2	0.0665 (12)	0.0895 (14)	0.0450 (10)	0.0326 (10)	−0.0159 (9)	−0.0296 (9)
O3	0.0440 (9)	0.0566 (10)	0.0404 (8)	0.0059 (7)	0.0040 (7)	−0.0128 (7)
C8	0.0501 (13)	0.0502 (13)	0.0466 (13)	0.0038 (10)	0.0108 (10)	−0.0117 (10)
C9	0.0488 (14)	0.0522 (13)	0.0484 (14)	0.0053 (11)	0.0105 (11)	0.0014 (11)
C10	0.0548 (14)	0.0587 (15)	0.0505 (14)	−0.0049 (12)	0.0034 (11)	0.0047 (11)
Cl1	0.0576 (4)	0.0596 (4)	0.0501 (4)	0.0019 (3)	−0.0152 (3)	−0.0042 (3)

Geometric parameters (Å, º)

C1—O3	1.349 (3)	C7—O2	1.225 (3)
C1—C6	1.393 (3)	C7—O1	1.279 (3)
C1—C2	1.405 (3)	O1—H1	0.9752
C2—C3	1.392 (3)	O3—C8	1.430 (3)
C2—C7	1.488 (3)	C8—C9	1.481 (3)
C3—C4	1.378 (3)	C8—H8A	0.9700
C3—H3	0.9300	C8—H8B	0.9700
C4—C5	1.373 (3)	C9—C10	1.303 (3)
C4—Cl1	1.738 (2)	C9—H9	0.9300
C5—C6	1.375 (4)	C10—H10A	0.9300
C5—H5	0.9300	C10—H10B	0.9300
C6—H6	0.9300
O3—C1—C6	123.2 (2)	O2—C7—O1	122.0 (2)
O3—C1—C2	117.89 (18)	O2—C7—C2	122.61 (19)
C6—C1—C2	118.9 (2)	O1—C7—C2	115.36 (19)
C3—C2—C1	119.37 (19)	C7—O1—H1	110.9
C3—C2—C7	117.91 (19)	C1—O3—C8	118.45 (17)
C1—C2—C7	122.72 (19)	O3—C8—C9	108.60 (19)
C4—C3—C2	120.3 (2)	O3—C8—H8A	110.0
C4—C3—H3	119.8	C9—C8—H8A	110.0
C2—C3—H3	119.8	O3—C8—H8B	110.0
C5—C4—C3	120.4 (2)	C9—C8—H8B	110.0
C5—C4—Cl1	120.26 (17)	H8A—C8—H8B	108.4
C3—C4—Cl1	119.34 (18)	C10—C9—C8	126.1 (2)
C4—C5—C6	120.2 (2)	C10—C9—H9	116.9
C4—C5—H5	119.9	C8—C9—H9	116.9
C6—C5—H5	119.9	C9—C10—H10A	120.0
C5—C6—C1	120.7 (2)	C9—C10—H10B	120.0
C5—C6—H6	119.6	H10A—C10—H10B	120.0
C1—C6—H6	119.6