Which of the following is second ion is more stable than the first

Options

A. `underset("I")(CH_(2)=Coverset(Theta)H) and underset("II")(CH=overset(theta)C)`
B. `underset("I")(C_(6)H_(5)-Coverset(Theta)H_(2)) and underset("II")(CH_(2)=CH-Coverset(Theta)H_(2))`
C. `CH_(3)-Coverset(Theta)H-CH=CH_(2) and Coverset(Theta)H_(2)-CH=CH_(2)`
D.

Answer

To determine which of the following second ions is more stable than the first, we will analyze the stability of carbanions formed from different compounds.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- We have four options (A, B, C, D) with different structures. We need to analyze the stability of the carbanions formed from these compounds.

2. **Analyze Option A**:
- The first compound is a vinylic carbonyl (CH2=CH-) and the second is an acetylenic carbonyl (CH≡C-).
- The acetylenic carbon has an sp-hybridized carbon, which has 50% s-character, making it more acidic and thus forming a more stable carbanion (CH≡C-).
- The vinylic carbon has an sp²-hybridized carbon with 33.33% s-character, making it less stable.
- **Conclusion**: The second ion (CH≡C-) is more stable than the first (CH2=CH-).

3. **Analyze Option B**:
- The first species is a benzylic carbanion (C6H5-CH2-) which can resonate through the benzene ring, forming four resonating structures.
- The second species is CH2=CH-CH2-, which has only two resonating structures.
- More resonating structures indicate greater stability.
- **Conclusion**: The first ion (C6H5-CH2-) is more stable than the second (CH2=CH-CH2-).

4. **Analyze Option C**:
- The first species is CH3-CH- (with a negative charge) and the second species is CH2=CH-CH2-.
- The CH3 group has a +I effect, which destabilizes the carbanion by increasing electron density.
- The second species does not have this destabilizing effect.
- **Conclusion**: The second ion (CH2=CH-CH2-) is more stable than the first (CH3-CH-).

5. **Analyze Option D**:
- The first compound has a double bond and a negative charge, making it aromatic (follows Huckel's rule with 6 π electrons).
- The second compound is aliphatic and does not have aromaticity.
- Aromatic compounds are generally more stable than aliphatic compounds.
- **Conclusion**: The first ion is more stable than the second.

### Final Conclusion:
The only option where the second ion is more stable than the first is **Option A** and **Option C**.