Q. Which of the following is the most stable carbanion?

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A

$CH_{3}\overset{\ominus}{C}H_{2}$

B

$\left(\left(\text{(CH}\right)_{\text{3}} \text{)}\right)_{2} \text{C} \overset{\ominus}{\text{H}}$

C

$CH_{3}\overset{-}{C}$

D

$C_{6}H_{5}\overset{-}{C}H_{2}$

Solution:

Benzyl carbanion is stabilized by resonance.

electron-releasing groups (+I groups) make the carbanion less stable. Thus, a primary carbanion is more stable than secondary carbanion, which in turn, is more stable than a tertiary, because of +I effect associated with alkyl groups. Decreasing order of stabilities of carbanion is

Electron-attracting groups (-I groups) like $-NO_{2},-Br$ will stabilize carbanion by partial removal of the negative charge on the carbon.

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