Question

Among the following which is / are more stable than $CH_2=CH-CH_2^{\ominus}$

• A. $CH_3^{\ominus}$
• B. Cyclohexadienyl carbanion
• C. $Ph_2CH^{\ominus}$
• D. $PhCH_2^{\ominus}$

Answer 1

Answer: (B), (C), (D)

$Ph_2CH^{\ominus}$, $PhCH_2^{\ominus}$, Cyclohexadienyl carbanion

Answer 2

The stability of carbanions is determined by factors like resonance, inductive effects, and hybridization. The allyl carbanion ($CH_2=CH-CH_2^{\ominus}$) is stabilized by resonance delocalization over two carbons.

1. $CH_3^{\ominus}$: Less stable due to lack of resonance and electron-donating alkyl groups.
2. Cyclohexadienyl carbanion: Resonance stabilization within the ring system makes it more stable than allyl.
3. $Ph_2CH^{\ominus}$: Highly stable due to extensive resonance delocalization into two phenyl rings.
4. $PhCH_2^{\ominus}$: More stable than allyl due to resonance delocalization into one phenyl ring.

Thus, $Ph_2CH^{\ominus}$, $PhCH_2^{\ominus}$, and the cyclohexadienyl carbanion are more stable than $CH_2=CH-CH_2^{\ominus}$.