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The hydrocarbon benzene has six carbon atoms arranged at the vertices of a regular hexagon, and six hydrogen atoms, with one bonded to each carbon atom.

I know that two molecules are said to be isomers if they are composed of the same number and types of atoms, but have different structure.

How many isomers may be obtained by replacing two of the hydrogen atoms with chlorine atoms, and two others with bromine atoms?

Show that exactly three isomers (ortho-dichlorobenzene, meta-di-chlorobenzene, and para-dichlorobenzene) may be constructed by replacing two of the hydrogen atoms of benzene with chlorine atoms.

So far I've ended up nowhere, I would appreciate the help.

3 Answers 3