2,4,6-Tri­methoxy­benzoic acid

In the crystal structure of 2,4,6-tri­methoxy­benzoic acid, C₁₀H₁₂O₅, the mol­ecules form hydrogen-bonded chains. The carboxyl group is in a syn conformation. The lone pair of electrons acting as the hydrogen bond acceptor is in an anti orientation.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.046
• wR factor = 0.150
• Data-to-parameter ratio = 22.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Ortho-alkoxy benzoic acids are a class of acids which crystallize with different packing modes. The singularity of 2-ethoxybenzoic acid which forms monomers is due to the formation of an intramolecular hydrogen bond (Gopalakrishna & Cartz, 1972). 2,3-Dimethoxybenzoic acid forms the normal acid dimer pattern (Bryan & White, 1982a). 2,6-Dimethoxybenzoic acid (Bryan & White, 1982b) and 2,6-dimethoxy-3-nitrobenzoic acid (Frankenbach et al., 1991) form catemers. The carboxyl group of 2,6-dimethoxybenzoic acid exists in an anti conformation, the carboxyl group of 2,6-dimethoxy-3-nitrobenzoic acid in a syn conformation. In 2,4,6-trimethoxybenzoic acid, (I), the three methoxy groups are nearly coplanar with the benzene ring (C5—C6—O61—C61 = 7.7°, C5—C4—O41—C41 = -7.0° and C3—C2—O21—C21 = 4.2°). As observed in 2,6-dimethoxybenzoic acid or 2,6-dimethoxy-3-nitrobenzoic acid, the hydrogen interaction from the hydroxyl O11 of one molecule to the remote carbonyl O12 of a neighbour (Table 2) form catemers. The torsion angle between the plane of the acid group and the benzene ring (C6—C1—C11—O12) is 54.1 (1)°, quite similar to the one found in 2,6-dimethoxybenzoic acid. However, in 2,4,6-trimethoxybenzoic acid, we find a syn-anti hydrogen-bond mode and in 2,6-dimethoxybenzoic acid an anti-anti hydrogen-bond mode. So the hypothesis (Frankenbach et al., 1991) of the stabilization of the anti-anti mode by an intramolecular hydrogen bond has to be rejected. More subtle packing effects in the environment of the hydroxyl group have to be considered to give a rational explanation.

S2. Experimental

2,4,6-Trimethoxybenzoic acid was purchased from Lancaster Chemicals. Crystals suitable for X-ray study were obtained from an ethanol solution by slow evaporation

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLUTON93 (Spek, 1993); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1.

2,4,6-trimethoxybenzoic acid

Crystal data

C10H12O5	F(000) = 448
Mr = 212.20	Dx = 1.382 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 10.602 (3) Å	Cell parameters from 25 reflections
b = 7.288 (1) Å	θ = 2.4–30.4°
c = 13.224 (8) Å	µ = 0.11 mm^−1
β = 93.80 (2)°	T = 293 K
V = 1019.6 Å^3	Prismatic, white
Z = 4	0.67 × 0.35 × 0.22 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	2256 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.047
Graphite monochromator	θmax = 30.4°, θmin = 2.4°
ω/2θ scans	h = 0→15
Absorption correction: ψ scan (North et al., 1968)	k = 0→10
Tmin = 0.907, Tmax = 0.976	l = −18→18
3231 measured reflections	3 standard reflections every 0 reflections
3083 independent reflections	intensity decay: none

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)] = 0.046	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.150	H atoms treated by a mixture of independent and constrained refinement
S = 1.08	w = 1/[σ^2(Fo^2) + (0.1033P)^2] where P = (Fo^2 + 2Fc^2)/3
3083 reflections	(Δ/σ)max = 0.025
140 parameters	Δρmax = 0.45 e Å^−3
0 restraints	Δρmin = −0.23 e Å^−3

Special details

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
C1	0.73315 (9)	0.36377 (13)	−0.07968 (7)	0.0266 (2)
C2	0.82274 (10)	0.36144 (14)	0.00349 (8)	0.0303 (2)
C3	0.82491 (11)	0.49953 (16)	0.07552 (9)	0.0354 (3)
H3	0.8848	0.4983	0.1302	0.042*
C4	0.73623 (11)	0.64025 (15)	0.06498 (9)	0.0341 (2)
C5	0.64563 (10)	0.64555 (14)	−0.01513 (8)	0.0316 (2)
H5	0.5862	0.7395	−0.0204	0.038*
C6	0.64542 (10)	0.50757 (14)	−0.08744 (8)	0.0271 (2)
C11	0.73508 (10)	0.22603 (13)	−0.16205 (8)	0.0276 (2)
C21	0.99718 (14)	0.2084 (2)	0.08982 (12)	0.0533 (4)
H21A	1.0487	0.3169	0.0931	0.080*
H21B	1.0497	0.1027	0.0821	0.080*
H21C	0.9541	0.1971	0.1511	0.080*
C41	0.66646 (18)	0.9259 (2)	0.13002 (12)	0.0566 (4)
H41A	0.6771	0.9832	0.0658	0.085*
H41B	0.6892	1.0110	0.1836	0.085*
H41C	0.5798	0.8898	0.1338	0.085*
C61	0.47554 (12)	0.64856 (19)	−0.18568 (11)	0.0441 (3)
H61A	0.4195	0.6560	−0.1317	0.066*
H61B	0.4271	0.6309	−0.2489	0.066*
H61C	0.5232	0.7602	−0.1884	0.066*
O11	0.72402 (11)	0.05480 (11)	−0.13116 (6)	0.0433 (2)
H11	0.7368	−0.0153	−0.1779	0.065*
O12	0.74446 (9)	0.26453 (11)	−0.25016 (6)	0.0407 (2)
O21	0.90670 (9)	0.22110 (13)	0.00537 (7)	0.0452 (3)
O41	0.74551 (10)	0.76822 (13)	0.14033 (7)	0.0506 (3)
O61	0.55990 (8)	0.49783 (12)	−0.16796 (6)	0.0368 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0304 (5)	0.0209 (4)	0.0279 (4)	0.0036 (3)	−0.0018 (4)	−0.0007 (3)
C2	0.0318 (5)	0.0262 (5)	0.0322 (5)	0.0069 (4)	−0.0034 (4)	−0.0003 (4)
C3	0.0369 (6)	0.0345 (5)	0.0333 (5)	0.0053 (4)	−0.0085 (4)	−0.0054 (4)
C4	0.0391 (6)	0.0295 (5)	0.0331 (5)	0.0021 (4)	−0.0012 (4)	−0.0076 (4)
C5	0.0330 (5)	0.0254 (5)	0.0358 (5)	0.0079 (4)	−0.0010 (4)	−0.0039 (4)
C6	0.0270 (4)	0.0244 (4)	0.0294 (4)	0.0026 (4)	−0.0023 (3)	−0.0001 (4)
C11	0.0311 (5)	0.0203 (4)	0.0311 (5)	0.0035 (3)	−0.0010 (4)	−0.0003 (3)
C21	0.0524 (8)	0.0506 (8)	0.0540 (8)	0.0206 (7)	−0.0194 (6)	0.0012 (6)
C41	0.0777 (10)	0.0409 (7)	0.0503 (8)	0.0190 (7)	−0.0020 (7)	−0.0183 (6)
C61	0.0372 (6)	0.0395 (6)	0.0538 (7)	0.0137 (5)	−0.0109 (5)	0.0025 (5)
O11	0.0761 (6)	0.0195 (4)	0.0344 (4)	−0.0005 (4)	0.0053 (4)	−0.0002 (3)
O12	0.0667 (6)	0.0261 (4)	0.0298 (4)	0.0062 (4)	0.0063 (4)	0.0009 (3)
O21	0.0450 (5)	0.0399 (5)	0.0482 (5)	0.0212 (4)	−0.0162 (4)	−0.0086 (4)
O41	0.0632 (6)	0.0424 (5)	0.0440 (5)	0.0143 (5)	−0.0134 (4)	−0.0212 (4)
O61	0.0360 (4)	0.0328 (4)	0.0396 (4)	0.0101 (3)	−0.0131 (3)	−0.0057 (3)

Geometric parameters (Å, º)

C1—C6	1.4005 (13)	C5—C6	1.3876 (14)
C1—C2	1.4050 (13)	C6—O61	1.3538 (12)
C1—C11	1.4824 (14)	C11—O12	1.2089 (13)
C2—O21	1.3551 (13)	C11—O11	1.3207 (12)
C2—C3	1.3848 (15)	C21—O21	1.4262 (15)
C3—C4	1.3921 (16)	C41—O41	1.4234 (16)
C4—O41	1.3636 (13)	C61—O61	1.4261 (14)
C4—C5	1.3826 (15)
C6—C1—C2	118.54 (9)	C4—C5—C6	118.50 (9)
C6—C1—C11	119.63 (8)	O61—C6—C5	123.39 (9)
C2—C1—C11	121.70 (9)	O61—C6—C1	115.17 (9)
O21—C2—C3	123.71 (9)	C5—C6—C1	121.41 (9)
O21—C2—C1	115.64 (9)	O12—C11—O11	122.14 (9)
C3—C2—C1	120.61 (9)	O12—C11—C1	123.85 (9)
C2—C3—C4	119.09 (10)	O11—C11—C1	114.01 (9)
O41—C4—C5	123.62 (10)	C2—O21—C21	118.05 (10)
O41—C4—C3	114.52 (10)	C4—O41—C41	117.94 (10)
C5—C4—C3	121.85 (10)	C6—O61—C61	117.96 (9)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O11—H11···O12^i	0.82	1.88	2.6683 (12)	160

Symmetry code: (i) −x+3/2, y−1/2, −z−1/2.