Final answer:
Dimethyl substituted benzenes are called xylene and have three possible isomers: ortho-xylene, meta-xylene, and para-xylene.
Step-by-step explanation:
Dimethyl substituted benzenes are called xylene. In the systematic nomenclature, the positions of the two methyl groups are indicated using numbers, resulting in three possible isomers: 1,2-dimethylbenzene, 1,3-dimethylbenzene, and 1,4-dimethylbenzene. However, in common nomenclature, the prefixes ortho-, meta-, and para- are used to describe their relative positions. If the two methyl groups are adjacent to each other, it is commonly called ortho-xylene (o-xylene). If they are across from each other, it is commonly called para-xylene (p-xylene). When the arrangement is intermediate between ortho- and para-, it is called meta-xylene (m-xylene).