aryl group (ârˈĭl) [key], in chemistry, group of atoms derived from benzene or from a benzene derivative by removing one hydrogen that is bonded to the benzene ring (see radical). The simplest aryl group is phenyl, C6H5 ; it is derived from benzene. The tolyl group, CH3C6H4, is derived from toluene (methylbenzene). The xylyl group, (CH3)2C6H3, is derived from xylene (dimethylbenzene). Just as several different alkyl groups may be derived from certain alkanes, so may several aryl groups be derived from certain aromatic compounds; for example, three different tolyl groups can be formed from toluene by removing hydrogen from different locations relative to the methyl group. When a functional group is joined with an aryl group, replacing the hydrogen that had been removed, a compound is formed whose characteristics depend largely on the functional group.