How many structural isomers are possible when one of the hydrogen is replaced by a chlorine atom in anthracene?

Options

A. 3
B. 7
C. 4
D. 6

Explanation

To determine how many structural isomers are possible when one of the hydrogen atoms in anthracene is replaced by a chlorine atom, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Anthracene**:
- Anthracene consists of three fused benzene rings. The structure can be represented as:
```
C1 C2 C3
/ \ / \ / \
C4 C5 C6 C7 C8
\ / \ / \ /
C9 C10 C11
```
- Each carbon atom in anthracene is sp² hybridized, and most of them are bonded to a hydrogen atom.

2. **Identify the Positions of Hydrogen Atoms**:
- In anthracene, the hydrogen atoms are located on the outer carbons (C1, C2, C3, C4, C5, C6, C9, C10, C11). However, the carbons at the fused junctions (C4, C5, C6) do not have hydrogen atoms.

3. **Replace Hydrogen with Chlorine**:
- When replacing one hydrogen atom with a chlorine atom, we can do this at various positions. However, due to the symmetry of the anthracene structure, some positions will lead to identical structures.

4. **Identify Equivalent Positions**:
- The positions can be numbered as follows:
- Position 1: C1
- Position 2: C2
- Position 3: C3
- Position 4: C9
- Position 5: C10
- Position 6: C11
- Positions 1, 2, and 3 are equivalent due to the symmetry of the structure, and similarly, positions 4, 5, and 6 are also equivalent.

5. **Count Unique Structural Isomers**:
- When we replace a hydrogen atom at positions 1, 2, or 3, we get the same structural isomer. Therefore, these three positions contribute to one unique isomer.
- Similarly, replacing a hydrogen at positions 4, 5, or 6 gives another unique isomer.
- Thus, we can conclude that there are two unique structural isomers when one hydrogen atom is replaced by chlorine in anthracene.

### Final Answer:
The total number of structural isomers possible when one hydrogen in anthracene is replaced by a chlorine atom is **2**.