In organic chemistry, a phenacyl group is an aromatic substituent that consists of a phenyl group attached to an acyl group. A molecule containing a phenacyl group has the formula RCH<sub>2</sub>(CO)C<sub>6</sub>H<sub>5</sub> and the structure shown to the right. Here, R denotes the remainder of the molecule; for instance, if R is Br, then the compound could be called "phenacyl bromide". Note however that in the standard IUPAC nomenclature this compound would instead be called "2-bromo-1-phenylethanone".