Which of the following carbanions are not resonance stabilized?

Options

A.
B.
C.
D.

Explanation

To determine which carbanions are not resonance stabilized, we need to analyze the structures provided in the options. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Understand Resonance Stabilization
Resonance stabilization occurs when a molecule can be represented by two or more valid Lewis structures (resonance structures) that contribute to the overall hybrid structure. This stabilization is typically seen in structures where negative charges can be delocalized over multiple atoms.

### Step 2: Analyze Each Carbanion
We will analyze each carbanion provided in the options to determine if they can be resonance stabilized.

#### Option A: Carbanion with sp2 Hybridization
- **Structure Analysis**: If the carbanion is sp2 hybridized, it can participate in resonance if it is planar.
- **Conclusion**: If the structure allows for resonance (i.e., if the negative charge can be delocalized), it is resonance stabilized.

#### Option B: Bridgehead Carbanion
- **Structure Analysis**: In a bridgehead structure, the sp2 hybridized carbon may not achieve planarity due to steric hindrance from the ring structure. This lack of planarity prevents effective resonance stabilization.
- **Conclusion**: This carbanion is **not resonance stabilized** due to the inability to achieve planarity.

#### Option C: Carbanion with Delocalization
- **Structure Analysis**: If the carbanion allows for the movement of electrons (negative charge) to adjacent atoms, it can participate in resonance.
- **Conclusion**: This carbanion is **resonance stabilized**.

#### Option D: Carbanion with Oxygen
- **Structure Analysis**: If the carbanion has a negative charge on an oxygen atom, and there are no empty orbitals available for resonance stabilization, it cannot effectively delocalize the negative charge.
- **Conclusion**: This carbanion is **not resonance stabilized**.

### Final Answer
The carbanions that are **not resonance stabilized** are:
- **Option B** (Bridgehead Carbanion)
- **Option D** (Carbanion with Oxygen)