2-Hy-droxy-6-isopropyl-3-methyl-benzoic acid.

The title compound, C11H14O3, is a multiple-substituted derivative of benzoic acid. Intracyclic C—C—C angles span a range of 117.16 (19)–122.32 (19)°. Apart from intramolecular hydrogen bonds between hydroxyl and carboxyl groups, intermolecular hydrogen bonds are present in the crystal structure, the latter ones giving rise to centrosymmetric carboxylic acid dimers.

The title compound, C 11 H 14 O 3 , is a multiple-substituted derivative of benzoic acid. Intracyclic C-C-C angles span a range of 117. 16 (19)-122.32 (19) . Apart from intramolecular hydrogen bonds between hydroxyl and carboxyl groups, intermolecular hydrogen bonds are present in the crystal structure, the latter ones giving rise to centrosymmetric carboxylic acid dimers.

Comment
Benzoic acid has found widespread use as a ligand in coordination chemistry for a variety of transition metals and elements from the s-and p-block of the periodic system of the elements. It can act as a neutral or -upon deprotonation -an anionic ligand and serve as mono-or bidentate ligand. By varying the substituents on the phenyl moiety, the acidity of the carboxylic acid group can be fine-tuned. Particular interest rests in benzoic acid derivatives showing an asymmetric pattern of substituents on the aromatic moiety due to different possible orientations of the ligand in coordination compounds and the possible formation of stereoisomeric products. At the beginning of a comprehensive study aimed at rationalizing the coordination behaviour of various benzoic acid derivatives towards a number of transition metals in dependence of the pH value of the reaction batches it seemed interesting to determine the crystal structure of the title compound to enable comparative studies.
C-C-C angles within the carbocyclic ring span a range of 117-122°. The two smallest angles are found on the C atoms bearing the alkyl substituents while the two biggest angles are found on the C atom bearing the hydroxyl group and the C atom in para-position to the one bonded to the alcoholic hydroxyl group.
While the isopropyl group is tilted significantly in relation to the benzene moiety, the carboxylic acid group is nearly in plane with the carbocycle. The least-squares planes defined by the C atoms of the isopropyl group as well as the C atoms of the benzene group, respectively, enclose an angle of 74.17 (9)°, while the least-squares planes defined by the atoms of the carboxylic acid group on the one hand and the carbon atoms of the aromatic moiety on the other hand intersect at an angle of only 7.07 (28)° (Fig. 1).
In the crystal structure, intra-as well as intermolecular hydrogen bonds can be observed. The intramolecular hydrogen bonds are formed by the H atom of the alcoholic hydroxyl group as the donor and the carbonylic O atom of the carboxylic acid group as the acceptor. The intermolecular hydrogen bonds are apparent between carboxylic acid groups connecting two neighbouring molecules to centrosymmetric dimers. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for the intramolecular motif is S 1 1 (6) on the unitary level while the intermolecular hydrogen bonds necessitate a R 2 2 (8) descriptor on the same level (Fig. 2). The shortest C g ···C g distance for benzene rings in the crystal was measured at 4.9918 (13) Å.
The packing of the title compound is shown in Figure 3.

Experimental
The compound was obtained commercially (Aldrich). Crystals suitable for the X-ray diffraction study were taken directly from the provided product.
supplementary materials sup-2 Refinement Carbon-bound H-atoms were placed in calculated positions (C-H 0.95 Å for aromatic C atoms, C-H 1.00 Å for the methine group and C-H 0.98 Å for methyl groups) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2U eq (C) or 1.5U eq (C). Oxygen-bound H-atoms were placed in calculated positions with O-H = 0.84 Å and U iso (H) = 1.5U eq (O). The methyl groups were allowed to rotate with a fixed angle around the C-C bonds to best fit the experimental electron density [AFIX 137 in the SHELX program suite (Sheldrick, 2008)]. The H atom of the carboxylic acid group as well as the hydroxyl group were allowed to rotate with a fixed angle around the C-O bonds to best fit the experimental electron density [AFIX 147 in the SHELX program suite (Sheldrick, 2008)]. Fig. 1. The molecular structure of the title compound, with anisotropic displacement ellipsoids drawn at 50% probability level.