 So, a given substituted phenyl compound has three isomers, "ortho" (1,2-disubstitution), "meta" (1,3-disubstitution) and "para" (1,4-disubstitution).A disubstituted phenyl compound (trisubstituted benzene) may be, for example, 1,3,5-trisubstituted, or 1,2,3-trisubstituted.Higher degrees of substitution, of which the pentafluorophenyl group is an example, exist, and are named according to IUPAC nomenclature.