Redetermination of 3,5-dimethylphenol

The previous structure determination [Gillier-Pandraud et al. (1972 ▶). C. R. Acad. Sci. Ser. C, 275, 1495] of the title compound, C8H10O, did not report atomic coordinates. There are two molecules in the asymmetric unit, A and B, which both show approximate non-crystallographic C s symmetry. The intracyclic C—C—C angles cover the range 118.74 (12)–121.76 (13)°. In the crystal, molecules are linked by O—H⋯O hydrogen bonds, generating [001] C 2 2(4) chains such that molecules A and B alternate. There is no aromatic π–π stacking in the crystal as the shortest centroid–centroid distance is greater than 4.74 Å.


Comment
Phenol and derivatives are interesting bonding partners for a variety of transition metals and elements from the p-block of the periodic system. They can act as neutral or -upon deprotonation -as anionic monodentate ligands. Upon variation of the substituents on the aromatic system, a seemingly endless series of symmetric as well as asymmetric phenol derivatives featuring different steric pretenses and acidities of the hydroxyl-group are available. At the beginning of a larger study aimed at elucidating the coordination behaviour of various phenol-derivatives in dependence of pH-value and substitution pattern on the phenyl moiety, it seemed of interest to determine the crystal structure of the title compound to enable comparisons with metric parameters in envisioned coordination compounds. Although the structure has been deposited with the Cambridge Structural Database (Gillier-Pandraud et al., 1972), no three-dimensional-coordinates were provided.
The asymmetric unit comprises two molecules of the title compound which are nearly orientated perpendicular to each other. The least-squares planes defined by the C-atoms of the respective phenyl moieties intersect at an angle of 87.87 (4)°.
Intracyclic C-C-C angles span a range of 119-122 ° with the biggest angles invariably found on the C-atoms bearing the hydroxyl group and the C-atoms in para-position to these, respectively. The H-atoms of both hydroxyl groups are approximately in plane with the aromatic systems ( Fig. 1).
In the crystal structure, a set of cooperative hydrogen bonds connects the molecules to infinite chains along the crystallographic c-axis. Both molecules in the asymmetric unit participate alternately in these chains. In terms of graph-set analysis, the description of these intermolecular interactions necessitates a C 2 2 (4) descriptor on the binary level (Fig. 2). The closest distance between two centers of gravity was measured at 4.7437 (8) Å.
The packing of the title compound in the crystal structure is shown in Figure 3.

Experimental
The compound was obtained commercially (Fluka). Crystals suitable for the X-ray diffraction study were taken directly from the provided compound.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.98 Å for the methyl groups and C-H 0.95 Å for aromatic carbon atoms) and were included in the refinement in the riding model approximation, with U(H) set to 1.5U eq (C) for the methyl groups and 1.2U eq (C) for aromatic carbon atoms. The H atoms of the methyl groups were allowed to rotate with a fixed angle around the C-C bonds to best fit the experimental electron density (HFIX 137 in the SHELX program suite (Sheldrick, 2008)). The H atom of the hydroxyl groups were allowed to rotate with a fixed angle around the O-C bonds to best fit the experimental electron density (HFIX 147 in the SHELX program suite (Sheldrick, 2008)), their U(H) set to 1.5U eq (O).  Fig. 1. The molecular structure of the title compound, with anisotropic displacement ellipsoids drawn at 50% probability level.