Received 24 March 2004
Dimeric hydrogen bonding is present in the crystal structure of (2-methylphenoxy)acetic acid, C9H10O3, involving the carboxylate groups of centrosymmetrically related pairs of molecules. The structure is further stabilized by C-HO hydrogen bonding.
The title compound, (I), also known as (o-tolyloxy)acetic acid, has been described as an expectorant (Negwer, 1996), and several phenoxyacetic acid compounds are used as herbicides (Cserhati & Forgacs, 1998).
The atomic arrangement in (I) is shown in Fig. 1 and selected geometric parameters are given in Table 1. Apart from the H atoms, the molecule is essentially planar and the torsion angle with the greatest deviation from 0, or 180°, is C2-O1-C7-C8 = 175.6 (2)°.
Carboxylic acids normally form dimers or catemers and here, as expected for a simple monocarboxylic acid, dimers are formed by intermolecular hydrogen bonding involving the carboxylate groups. The pairs of molecules forming the dimers are related by a centre of symmetry and details of the hydrogen bonding are given in Table 2. As well as the dimeric R22(8) motif, a weak C-HO contact (Table 2) is present and this links two molecules about a centre of symmetry in an R22(14) formation (Fig. 2). Hence, atom O2 acts as both a donor and an acceptor. Indications of C-H bonding (Table 2) are also present as H7A is close to the centroid (Cg1) of the aromatic ring.
There are many similar examples of dimer formation involving carboxylate groups e.g. phenylacetic acid (Hodgson & Asplund, 1991) and 2,4,5-trimethylbenzoic acid (Barcon et al., 1997). The solid-state structures of related compounds, viz. (4-methylphenoxy)acetic acid (Kumar & Rao, 1982) and 3-(2-hydroxyphenyl)propionic acid (Begum et al., 1992), have also been determined.
| || Figure 1 |
The atomic arrangement in the molecule of (I), with the the atom-numbering scheme and 50% probability displacement ellipsoids.
| || Figure 2 |
A partial packing diagram of (I), showing R22(8) and R22(14) ring formations. [Symmetry codes: (*) -1 - x, -y, 1 - z; (#) -x, -y, 2 - z.]
The title compound was obtained from Aldrich and was recrystallized from a mixture of methanol and ethanol.
The crystal diffracted very weakly and decomposed during data collection, hence data completeness is only 71%. The hydroxy (O2) H atom was refined isotropically. The C-H H atoms were allowed to ride on their attached C atoms: C-H distances were 0.95 Å (aromatic), 0.99 Å (methylene) and 0.98 Å (methyl), and Uiso(H) = 1.2Ueq(non-methyl C) or 1.4Ueq(methyl C).
Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; 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); software used to prepare material for publication: WinGX (Farrugia, 1999).
We thank the EPSRC for use of the National Crystallographic Service at Southampton University (X-ray data collection) and for the use of the Chemical Database Service at Daresbury (Fletcher et al., 1996).
Altomare, A., Burla, M. C., Camalli, M., Cascarano, G., Giacovazzo, C., Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1999). J. Appl. Cryst. 32, 115-119.
Barcon, A., Cote, M. L., Brunskill,, A. P. J., Thompson, H. W. & Lalancette, R. A. (1997). Acta Cryst. C53, 1842-1845.
Begum, N. S., Jain, M., Chandrasekhar, S. & Venkatesan, K. (1992). Acta Cryst. C48, 1076-1078.
Blessing, R. H. (1995). Acta Cryst. A51, 33-38.
Cserhati, T. & Forgacs, E. (1998). J. Chromatogr. B, 717, 157-178.
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837-838.
Fletcher, D. A., McMeeking, R. F. & Parkin, D. (1996). J. Chem. Inf. Comput. Sci. 36, 746-749.
Hodgson, D. J. & Asplund, R. O. (1991). Acta Cryst. C47, 1986-1987.
Hooft, R. (1998). COLLECT. Nonius BV, Delft, The Netherlands.
Kumar, S. V. & Rao, L. M. (1982). Z. Kristallogr. 161, 45-51.
Negwer, M. (1996). Organic Chemical Drugs and their Synonyms. 7th ed., Vol. 1. Berlin: Akademie Verlag.
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr and R. M. Sweet, pp. 307-326. New York: Academic Press.
Sheldrick, G. M. (1997). SHELXL97. University of Göttingen, Germany.
Spek, A. L. (2003). J. Appl. Cryst. 36, 7-13.