Which of the following are not ambident carbanions ?

Options

A.
B. `overset(ɵ)(C)H_(2)-CH=O`
C.
D.

Explanation

To determine which of the given options are not ambident carbanions, we need to analyze each option based on the criteria for ambident carbanions. An ambident carbanion is characterized by the following:

1. The carbanion must be capable of resonance.
2. There should be more than one different canonical structure.

Now, let's analyze each option step by step.

### Step 1: Analyze Option A (CH2-)
- **Structure**: CH2- has a negative charge on carbon.
- **Resonance**: There are no conjugate double bonds or other atoms that can stabilize the negative charge through resonance.
- **Conclusion**: Since there is no resonance, this is not an ambident carbanion.

### Step 2: Analyze Option B (CH2=O-)
- **Structure**: CH2=O- has a double bond between carbon and oxygen, with a negative charge on carbon.
- **Resonance**: The negative charge can be delocalized to the oxygen, forming different canonical structures (one with the negative charge on carbon and another with the negative charge on oxygen).
- **Conclusion**: This is an ambident carbanion because it satisfies both conditions.

### Step 3: Analyze Option C
- **Structure**: This option has a carbanion with no conjugation near the negative charge.
- **Resonance**: Since there is no conjugation, resonance cannot occur.
- **Conclusion**: This is not an ambident carbanion.

### Step 4: Analyze Option D
- **Structure**: This option shows a structure with conjugation present.
- **Resonance**: The negative charge can be delocalized, leading to different canonical structures.
- **Conclusion**: This is an ambident carbanion.

### Final Conclusion
Based on the analysis:
- **Not Ambident Carbanions**: Option A (CH2-) and Option C.
- **Ambident Carbanions**: Option B (CH2=O-) and Option D.

### Answer:
The options that are not ambident carbanions are **Option A and Option C**.