Q65 / 180 · AIIMS 2012 · Chemistry

Assertion : $\mathrm{HC} \equiv \mathrm{C}^{-}$is more stable than $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$.Reason : $\mathrm{HC} \equiv \mathrm{C}^{-}$has more s-character than $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$

  • Correct answer
    A
    If both assertion and reason are true and reason is the correct explanation of assertion
  • B
    If both assertion and reason are true but reason is not the correct explanation of assertion
  • C
    If assertion is true but reason is false
  • D
    If both assertion and reason are false.

Solution

$\mathrm{HC} \equiv \mathrm{C}^{-}$has $50 \%$ s-character and $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$has $33 \%$ s-character. Stability of carbanions increases with an increase in the s-character at the carbanion. So $\mathrm{HC} \equiv \mathrm{C}^{-}$is more stable than $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$.

Hence, the correct answer is option: 'A'.

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