3-(4-Bromo-phen-yl)cyclo-pent-2-en-1-one.

In the title compound, C11H9BrO, the cyclo-pentenone ring is almost planar with an r.m.s. deviation of 0.0097 Å. The largest inter-ring torsion angles [2.4 (3), 1.3 (3) and 3.53 (2)°] reveal only a very small twist between the rings, and suggest that the two rings are conjugated. The mol-ecule is slightly bowed, as shown by the small dihedral angle between the rings [5.3 (1)°]. The crystal packing pattern consists of parallel sheets that stack parallel to the ac plane. Each sheet consists of mol-ecules that pack side-to-side with the same relative orientation of phenyl and cyclo-pentenone rings along the a- and c-axis directions. Slipped side-to-side, face-to-face and edge-to-face inter-actions exist between pairs of sheets with edge-to-edge and edge-to-face O⋯H-C(sp (2)) weak hydrogen-bond contacts. A relatively short edge-to-face contact (2.77 Å) also exists between pairs of sheets.