Which of the following can not be prepared by Williamson's synthesis ?

Options

A. Methoxybenzene
B. Benzyl-p-nitrophenyl ether
C. Methyl tert-butyl ether
D. Di-tertiary butly ether.

Explanation

To determine which compound cannot be prepared by Williamson's synthesis, we need to understand the mechanism and limitations of this reaction.

### Step-by-Step Solution:

1. **Understanding Williamson's Synthesis**:
- Williamson's synthesis is a method for preparing ethers. It involves the reaction of an alkoxide ion (RO-) with a primary alkyl halide (R'X) to form an ether (R-O-R').
- The general reaction can be represented as:
\[ R-O^- + R'X \rightarrow R-O-R' + X^- \]

2. **Identifying the Reactants**:
- In Williamson's synthesis, the alkyl halide should ideally be a primary or sometimes a secondary halide. Tertiary alkyl halides are generally not suitable because they tend to undergo elimination reactions instead of substitution.

3. **Analyzing the Options**:
- We need to evaluate the given options to see which ether cannot be formed using Williamson's synthesis.
- If any option contains a tertiary alkyl halide, it is likely that it cannot be synthesized via this method.

4. **Recognizing the Limitation**:
- Tertiary alkyl halides lead to elimination reactions, resulting in the formation of alkenes rather than ethers. Therefore, ethers that would require tertiary alkyl halides in their synthesis cannot be formed through Williamson's synthesis.

5. **Conclusion**:
- Among the given options, if one of them is a di-tertiary butyl ether (which would require the use of a tertiary alkyl halide), it cannot be prepared by Williamson's synthesis. Thus, the answer is:
- **Di-tertiary butyl ether** cannot be prepared by Williamson's synthesis.

### Final Answer:
The compound that cannot be prepared by Williamson's synthesis is **di-tertiary butyl ether**.