Which of the following ketone does not react with `CH_(3)MgBr`?

Options

A. `CH_2-overset(O)overset(||)(C )-CH_3`
B. `C_6H_5-overset(O)overset(||)(C )-CH_3`
C.
D. `CH_3-CH_2-overset(O)overset(||)(C )-CH_3`

Answer

To determine which ketone does not react with `CH₃MgBr` (a Grignard reagent), we need to analyze the structure of each ketone and consider the steric hindrance that may prevent the Grignard reagent from attacking the carbonyl carbon.

### Step-by-Step Solution:

1. **Understanding Grignard Reagents**:
- Grignard reagents, such as `CH₃MgBr`, contain a carbon atom that carries a negative charge (nucleophile) and can react with electrophilic centers, such as the carbonyl carbon in ketones.

2. **Identifying the Ketones**:
- We need to examine the structures of the ketones provided in the options. Generally, ketones have the structure `R-C(=O)-R'`, where R and R' can be various alkyl or aryl groups.

3. **Analyzing Steric Hindrance**:
- Steric hindrance occurs when bulky groups around the carbonyl carbon prevent the nucleophile (in this case, `CH₃⁻`) from effectively approaching and attacking the carbonyl carbon.
- If R and R' are small groups (like methyl or ethyl), the Grignard reagent can easily attack the carbonyl carbon.
- If R or R' is a bulky group (like a tertiary butyl group), it can hinder the approach of the Grignard reagent.

4. **Evaluating Each Option**:
- **Option A**: Contains small alkyl groups (e.g., methyl). This ketone will react with `CH₃MgBr`.
- **Option B**: Contains a phenyl group and a methyl group. This ketone will also react with `CH₃MgBr` as the groups are not bulky.
- **Option C**: Contains a tertiary butyl group and a benzene ring with two methyl groups at the ortho positions. The bulky nature of the tertiary butyl group and the steric hindrance from the ortho methyl groups will prevent the Grignard reagent from attacking the carbonyl carbon.
- **Option D**: Contains small alkyl groups (e.g., ethyl and methyl). This ketone will react with `CH₃MgBr`.

5. **Conclusion**:
- The ketone that does not react with `CH₃MgBr` is the one in **Option C**, due to significant steric hindrance caused by the bulky groups.

### Final Answer:
**C** (the ketone with a tertiary butyl group and a benzene ring with ortho methyl groups) does not react with `CH₃MgBr`.