How many tetramethyl benzene are possible:

Answer

To determine how many tetramethylbenzene isomers are possible, we need to analyze the placement of four methyl groups on a benzene ring. Here's a step-by-step breakdown of the solution:

### Step 1: Understand the Structure of Benzene
Benzene is a six-carbon ring with alternating double bonds. The molecular formula is C6H6. When we add four methyl groups (–CH3) to the benzene ring, we create tetramethylbenzene.

### Step 2: Identify Possible Positions for Methyl Groups
The benzene ring has six carbon atoms, which we can number from 1 to 6. We need to place four methyl groups on these carbon atoms. The positions of the methyl groups will determine the different isomers.

### Step 3: Consider Different Arrangements
1. **1,2,3,4-Tetramethylbenzene**: Place methyl groups on adjacent carbons (1, 2, 3, and 4).
2. **1,2,3,5-Tetramethylbenzene**: Move one methyl group from position 4 to position 5 (1, 2, 3, and 5).
3. **1,2,4,5-Tetramethylbenzene**: Place methyl groups on positions 1, 2, 4, and 5, leaving position 3 empty.
4. **1,3,4,5-Tetramethylbenzene**: Place methyl groups on positions 1, 3, 4, and 5.

### Step 4: Count the Unique Isomers
By analyzing the arrangements, we find the following unique isomers:
- 1,2,3,4-Tetramethylbenzene
- 1,2,3,5-Tetramethylbenzene
- 1,2,4,5-Tetramethylbenzene
- 1,3,4,5-Tetramethylbenzene

### Conclusion
In total, there are **four structural isomers** of tetramethylbenzene possible.