Passage
Organic compounds mainly consist of covalent bonds. The electron pair in these covalent bonds may undergo displacement either of their own or under the influence of other species. The cleavage of covalent bond between two atoms takes place in homolytic or heterolytic fashion. The homolytic fission results into free radicals while heterolytic fission results into carbocations and carbanions. These are also called reaction intermediates and are attacked by electrophiles and nucleophiles. The electrophiles seek electron rich sites while nucleophiles seek electron deficient sites.
Answer the followings Questions :
The most stable carbanion among the following is

Options

A.
B.
C.
D.

Answer

To determine the most stable carbanion from the given options, we need to analyze the effects of substituents on the stability of the carbanion. Here’s a step-by-step solution:

### Step 1: Identify the Carbanions
We have four carbanions to evaluate:
1. CH2^-
2. CH2^- with an electron-donating group (e.g., CH3)
3. CH2^- with an electron-withdrawing group (e.g., OCH3)
4. CH2^- with a strong electron-withdrawing group (e.g., NO2)

### Step 2: Understand the Stability Factors
The stability of carbanions is influenced by:
- **Electron-withdrawing groups (EWGs)**: These groups stabilize negative charges by pulling electron density away from the carbanion.
- **Electron-donating groups (EDGs)**: These groups destabilize carbanions by increasing electron density at the negatively charged carbon.

### Step 3: Analyze Each Carbanion
1. **CH2^-**: This carbanion has no substituents, so it has a moderate stability.
2. **CH2^- with CH3**: The CH3 group is an EDG, which increases electron density and destabilizes the carbanion.
3. **CH2^- with OCH3**: The OCH3 group has a lone pair that can donate electrons (through resonance), which also increases electron density and destabilizes the carbanion.
4. **CH2^- with NO2**: The NO2 group is a strong EWG. It pulls electron density away from the carbanion, stabilizing the negative charge.

### Step 4: Conclusion
Among the four carbanions, the one with the NO2 group is the most stable due to the strong electron-withdrawing effect of the NO2 group, which stabilizes the negative charge on the carbanion.

### Final Answer
The most stable carbanion among the given options is the one with the NO2 group (option 4).

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