**Structural Isomers in C6H6**

**Introduction:**
Structural isomers are compounds that have the same molecular formula but differ in the arrangement of atoms in the molecule. In the case of C6H6, the molecular formula indicates that there are 6 carbon atoms and 6 hydrogen atoms. Let's explore the possible structural isomers for C6H6.

**Explanation:**

**1. Benzene:**
Benzene is the most common and stable compound with the molecular formula C6H6. It consists of a hexagonal ring of carbon atoms, with each carbon atom bonded to one hydrogen atom. This structure is known as the cyclic structure of benzene.

**2. 1,2-Dimethylbenzene (o-Xylene):**
In this isomer, two methyl groups (-CH3) are attached to adjacent carbon atoms of the benzene ring. This isomer is called o-Xylene because the methyl groups are in the ortho (1,2) position relative to each other.

**3. 1,3-Dimethylbenzene (m-Xylene):**
In this isomer, two methyl groups (-CH3) are attached to carbon atoms that are one position apart in the benzene ring. This isomer is called m-Xylene because the methyl groups are in the meta (1,3) position relative to each other.

**4. 1,4-Dimethylbenzene (p-Xylene):**
In this isomer, two methyl groups (-CH3) are attached to carbon atoms that are two positions apart in the benzene ring. This isomer is called p-Xylene because the methyl groups are in the para (1,4) position relative to each other.

**Conclusion:**
In conclusion, there are four structural isomers of C6H6:
1. Benzene
2. 1,2-Dimethylbenzene (o-Xylene)
3. 1,3-Dimethylbenzene (m-Xylene)
4. 1,4-Dimethylbenzene (p-Xylene)

These isomers differ in the arrangement of atoms in the molecule, which results in distinct chemical and physical properties. It is important to note that these isomers have the same molecular formula (C6H6), but their structural arrangement is different.