Step 5: Repeat the process for tetra-, penta-, and hexachlorobenzenes. For tetrachlorobenzenes, there are three isomers: 1,2,3,4-tetrachlorobenzene, 1,2,3,5-tetrachlorobenzene, and 1,2,4,5-tetrachlorobenzene. For pentachlorobenzene, there is only one isomer due to symmetry. For hexachlorobenzene, all six hydrogen atoms are replaced by chlorine, resulting in a single compound.