Final answer:
Replacing a hydrogen atom with a chlorine atom in anthracene can yield multiple isomers. This is due to the presence of several nonequivalent positions in anthracene's structure, each capable of creating a unique substituted isomer. The exact number of structural isomers depends on the unique positions available for substitution.
Step-by-step explanation:
When one of the hydrogen atoms in anthracene is replaced by a chlorine atom, it is possible to create multiple structural isomers because anthracene has several nonequivalent positions for the substitution. Anthracene is a polycyclic aromatic hydrocarbon consisting of three fused benzene rings. Since there are different possible positions on the fused benzene rings where the hydrogen atom can be replaced, each position creates a unique structural isomer.
For instance, if a chlorine atom is added to any carbon in the central ring that is unique in the structure, the isomer formed would be unique as well. The same reasoning applies if chlorine is added to one of the outer benzene rings' positions that are not equivalent due to the overall symmetry of anthracene. Because anthracene has multiple such unique positions, the number of possible structural formulas for chlorinated anthracene will depend on these considerations.