4-Chloro-3-ethylphenol

The title compound, C8H9ClO, packs with two independent molecules in the asymmetric unit, without significant differences in corresponding bond lengths and angles, with the ethyl group in each oriented nearly perpendicular to the aromatic ring having ring-to-side chain torsion angles of 81.14 (18) and −81.06 (19)°. In the crystal, molecules form an O—H⋯O hydrogen-bonded chain extending along the b-axis direction, through the phenol groups in which the H atoms are disordered. These chains pack together in the solid state, giving a sheet lying parallel to (001), via an offset face-to-face π-stacking interaction characterized by a centroid–centroid distance of 3.580 (1) Å, together with a short intermolecular Cl⋯Cl contact [3.412 (1) Å].

The title compound, C 8 H 9 ClO, packs with two independent molecules in the asymmetric unit, without significant differences in corresponding bond lengths and angles, with the ethyl group in each oriented nearly perpendicular to the aromatic ring having ring-to-side chain torsion angles of 81.14 (18) and À81.06 (19) . In the crystal, molecules form an O-HÁ Á ÁO hydrogen-bonded chain extending along the b-axis direction, through the phenol groups in which the H atoms are disordered. These chains pack together in the solid state, giving a sheet lying parallel to (001), via an offset face-to-face -stacking interaction characterized by a centroid-centroid distance of 3.580 (1) Å , together with a short intermolecular ClÁ Á ÁCl contact [3.412 (1) Å ].

Comment
4-Chloro-3-ethylphenol, the title compound, can be synthesized by chlorination of 3-ethylphenol by SO 2 Cl 2 in the presence of FeCl 3 in CCl 4 (Awano et al., 1987) or by adding the hydroxyl group to 1-ethyl-2-nitrobenzene followed by an acidic workup and a Sandmeyer reaction with CuCl (Schroetter et al., 1977). The title compound has been found to be useful in multiple biological applications, including testing the contracture in malignant hypothermia skeletal tissue (Low et al., 1997) and in biological activity on Ca 2+ deposits in muscle cells (Gerbershagen et al., 2005).
The two independent molecules of the title compound in the asymmetric unit (  (Cox, 2003), and 4-chloro-3,5-dimethylphenol (Cox, 1995). The ethyl group is rotated nearly perpendicular to the plane of the ring for each independent molecule, displaying very similar torsion angles of 81.14 (18)° (C4-C3-C7-C8) and -81.06 (19)° (C12-C11-C15-C16). The structure forms a one-dimensional O-H···O hydrogen-bonded chain through the phenol groups, in which the phenol protons are 50% rotationally disordered (Fig. 2). These chains run parallel to the crystallographic b-axis. Each independent molecule forms hydrogen bonds with a neighboring equivalent independent molecule, with an oxygen-oxygen distance (O1···O1 i ) of 2.708 (3) Å and an oxygen-oxygen distance (O2···O2 ii ) of 2.704 (2) Å [for symmetry codes (i) and (ii), see Table 1]. These pairwise dimers are hydrogen-bonded to one another resulting in a third unique hydrogen bond, (O1···O2 i ), with length 2.6642 (17) Å. A similar hydrogen-bonding motif is found in the ordered one-dimensional hydrogen bonding chain in the structure of 4-chloro-3-methylphenol (Cox, 2003), where the O···O distances are similar at 2.711 (2) and 2.714 (2) Å. Unlike 4-chloro-3-methylphenol, where the planes of the aromatic units on each side of the hydrogen-bonded chain are parallel, in the the title compound they form a herringbone (edge-to-face or T) motif.
Neighboring hydrogen-bonded chains pack together in the solid state to form a two-dimensional sheet parallel to the 0 0 1 plane via an offset face-to-face π-stacking interaction of one of the two independent molecules, whereas the other molecule does not engage in π-stacking (Fig. 3). The π-stacking is characterized by a centroid-to-centroid distance of 3.580 (1) Å, a plane-to-centroid distance of 3.410 (1) Å, and a ring offset or ring-slipage distance of 1.092 (3) Å (Lueckheide et al., 2013). Neighboring sheets are further linked by a short intermolecular chlorine-chlorine contact (Cl1···Cl2 iii ) of 3.412 (1) Å, which is less than the sum of the van der Waals radii of 3.50 Å for chlorine-chlorine interactions (Pedireddi et al., 1994). For symmetry code (iii): -x, -y + 1, -z.

Refinement
All non-hydrogen atoms were refined anisotropically. Hydrogen atoms on carbon were included in calculated positions and refined using a riding model with C-H = 0.95, 0.98 and 0.99 Å and U iso (H) = 1.2, 1.5 and 1.2 × U eq (C) of the aryl, methyl and methylene C-atoms, respectively. The positions of the disordered phenolic hydrogen atoms were found in the difference map and refined semi-freely at 50% occupancy using a distance restraint d(O-H) = 0.84 Å, and U iso (H) = 1.2× U eq (O).  A view of the one-dimensional hydrogen-bonded chain extending along b, with displacement ellipsoids shown at the 50% probability level. For symmetry codes (i) and (ii), see Table 1.

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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.