Most stable carbanion is :-

Options

A. `HC -= bar (C )`
B. `H_(2)C = bar(CH)`
C. `CH_(3) - oversetoverset(CH_(3))(|)undersetunderset(CH_(3))(|)C-barCH_(2)`
D. `CH_(3) - undersetunderset(CH_(3))(|)CH-barCH_2`

Answer

To determine which carbanion is the most stable, we need to analyze the hybridization and the s-character of the carbanions provided. Here’s a step-by-step solution:

### Step 1: Identify the Carbanions
We are given four carbanions. Let's denote them as:
- Carbanion A: 1 sigma bond, 1 lone pair
- Carbanion B: 2 sigma bonds, 1 lone pair
- Carbanion C: 3 sigma bonds, 1 lone pair
- Carbanion D: 3 sigma bonds, 1 lone pair

### Step 2: Determine Hybridization
- **Carbanion A**:
- 1 sigma bond + 1 lone pair = Steric number 2
- Hybridization: sp
- **Carbanion B**:
- 2 sigma bonds + 1 lone pair = Steric number 3
- Hybridization: sp²
- **Carbanion C**:
- 3 sigma bonds + 1 lone pair = Steric number 4
- Hybridization: sp³
- **Carbanion D**:
- 3 sigma bonds + 1 lone pair = Steric number 4
- Hybridization: sp³

### Step 3: Calculate s-character
- **Carbanion A (sp)**:
- s-character = 50% (1 s orbital out of 2 total orbitals)
- **Carbanion B (sp²)**:
- s-character = 33.3% (1 s orbital out of 3 total orbitals)
- **Carbanion C (sp³)**:
- s-character = 25% (1 s orbital out of 4 total orbitals)
- **Carbanion D (sp³)**:
- s-character = 25% (1 s orbital out of 4 total orbitals)

### Step 4: Analyze Stability
The stability of carbanions is influenced by the s-character of the hybrid orbitals:
- Higher s-character means greater electronegativity and better ability to stabilize the negative charge.
- Carbanion A has the highest s-character (50%), followed by Carbanion B (33.3%), and both Carbanion C and D have the lowest s-character (25%).

### Conclusion
Since Carbanion A has the highest s-character, it is the most stable carbanion among the options provided.

**Final Answer: Carbanion A is the most stable carbanion.**