Question

Assertion (A): $Na^{+}(C_{5}H_{11})^{-}$ is more stable than $Na^{+}(C_{5}H_{5})^{-}$. Reason (R): $C_{5}H_{5}$ readily accept electron to become 6-electron aromatic $C_{5}H_{5}^{-}$.}

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is NOT the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Aromatic ions are always more stable than their non-aromatic/aliphatic counterparts.

Answer 1

The Correct Option is D

Step 1: Concept Aromaticity provides significant thermodynamic stability to ions. The Cyclopentadienyl anion ($C_{5}H_{5}^{-}$) follows Huckel's rule ($4n+2$).

Step 2: Meaning $C_{5}H_{5}^{-}$ has 6 $\pi$ electrons and is aromatic, making it extremely stable. $C_{5}H_{11}^{-}$ is a localized aliphatic carbanion, which is significantly less stable.

Step 3: Analysis The Assertion claims the aliphatic version is more stable, which is false. The Reason correctly states that the cyclopentadienyl radical accepts an electron to become a stable 6-electron aromatic anion.

Step 4: Conclusion Since the Assertion is false and the Reason is true, the correct choice is (D). Final Answer: (D)