Crystal structure of 1-[3,5-bis(trifluoromethyl)phenyl]-2-bromoethan-1-one

The title compound crystallizes with four molecules in the unit cell (Z = 4) and one formula unit in the asymmetric unit. In the crystal, molecules are linked in a head-to-tail fashion into dimers along the b-axis direction through weak C—H⋯Br and C—O⋯Csp 2 interactions. C—H⋯O, C—F⋯π and F⋯F interactions are also observed


Structural commentary
A displacement ellipsoid plot of the title compound with the atom labelling is shown in Fig. 1. The compound crystallizes in the monoclinic space group P2 1 /c with one molecule in the asymmetric unit and four molecules in the unit cell (Z = 4). The torsion angle between the alkyl bromide unit and the ISSN 2056-9890 phenyl ring (C3-C2-C1-Br1) is À179.6 (3) whereas that between the alkyl bromide and carbonyl parts (O1-C2-C1-Br1) is 0.3 (5) , which shows a preference for a syn orientation of the alkyl bromide unit with respect to the carbonyl group.

Database survey
There are more than 1000 crystal structure of phenyl ethanone derivatives in the Cambridge Structural Database (CSD) (Conquest Version 1.17; Groom et al., 2016) but none of them gave a hit for 1-[3,5-bis(trifluoromethyl)phenyl]-2-bromo-ethanone. However, the crystal structures of related derivatives have been reported. These include phenyl 2-bromoethanone (URELEJ; Betz et al., 2011) and a phenyl 2-bromoethanone complex (VIVFIP; Laube et al., 1991). The first compound, Z = 4, features two prominent hydrogen bonds involving the oxygen atom while in the second, also Z = 4, the oxygen atom forms a complex with antimony pentachloride.

Synthesis and crystallization
A stirred solution of 3,5-bis(trifluoromethyl) acetophenone (0.5 g, 1.95 mmol) in acetic acid (5 mL) was added dropwise to bromine (0.312 g, 1.95 mmol) in acetic acid. The reaction medium was stirred at room temperature for 5 h. To the resulting mixture, water (5 mL) was added and the mixture was concentrated under reduced pressure. The residue Dimer assembled through C-HÁ Á ÁBr and >C OÁ Á Á(>C O) interactions (left) and dimers extending along the b-axis direction via C-HÁ Á ÁO and C-FÁ Á Á interactions (Table 1).

Figure 3
FÁ Á ÁF interactions resulting in a bilayer that packs in a parallel fashion along the a-axis direction. Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The asymmetric unit of the title compound, with 50% probability ellipsoids.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.