Which of the following cannot be prepared by Sandmeyer's reaction?

Options

A. Chlorobenzene
B. Bromobenzene
C. Iodobenzene
D. Fluorobenzene

Explanation

To determine which of the following compounds cannot be prepared by Sandmeyer's reaction, we first need to understand the Sandmeyer's reaction itself.

### Step 1: Understand Sandmeyer's Reaction
Sandmeyer's reaction involves the conversion of benzene diazonium salts into aryl halides. The general reaction can be represented as follows:

\[ \text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- \xrightarrow{\text{CuX}_2} \text{C}_6\text{H}_5\text{X} + \text{N}_2 \]

Where \( X \) can be Cl or Br.

### Step 2: Identify the Halogens
In the Sandmeyer's reaction, the halogen \( X \) can only be chlorine (Cl) or bromine (Br). This means that:

- Chlorobenzene can be prepared using CuCl2.
- Bromobenzene can be prepared using CuBr2.

### Step 3: Determine Which Compounds Cannot Be Prepared
Now, we need to identify the halogens that cannot be used in this reaction:

- **Iodine (I)**: Cannot be prepared because there is no stable CuI2 salt available for the reaction.
- **Fluorine (F)**: Similarly, there is no stable CuF2 salt available for the reaction.

### Step 4: Conclusion
Based on the above analysis, the compounds that cannot be prepared by Sandmeyer's reaction are:

- Iodobenzene
- Fluorobenzene

Thus, the correct answer is that both **C (Iodobenzene)** and **D (Fluorobenzene)** cannot be prepared by Sandmeyer's reaction.

### Summary of the Solution
- Sandmeyer's reaction converts benzene diazonium salts to aryl halides using CuX2.
- Only Cl and Br can be used in this reaction.
- Iodobenzene and Fluorobenzene cannot be prepared using this method.