Question

There are several aromatic compounds with the formula `C_8H_9Cl`. What are three that have a disubstituted ring where the chlorine is not attached to the ring?

Answer 1

They have to be the ortho/meta/para isomers. "Not attached to the ring" only means not directly attached. It does not mean you have a chlorine atom somewhere, floating freely next to the compound.

Ortho (same side) means a 1,2 relationship between two aromatic substituents, meta means 1,3, and para (opposite sides) means 1,4.

A default aromatic ring is benzene, `"C"_6"H"_6`, so consider `"C"_6"H"_4` by default for a disubstituted aromatic ring without substituents and go from there. With two carbons and 5 hydrogens available, and the chlorine not directly on the ring...

• We can have `-"CH"_2"Cl"` as one substituent and `"CH"_3` as the other. This accounts for the remaining `"C"_2"H"_5` in the formula.
• We can move one of substituents around for the isomers.

Convince yourself that the formulas are still `"C"_8"H"_9"Cl"`. These are respectively called:

• o-chloromethyltoluene
• m-chloromethyltoluene
• p-chloromethyltoluene