Question

Hyperconjugation is not observed in:

• A. A free radical $(-\stackrel{\bullet }{C}{H}_2)$
• B. A carbanion $(-\stackrel{-}{C}{H}_2)$
• C. A carbocation $(-\stackrel{+}{C}{H}_2)$
• D. A double bond $\text{>C=C<}$

Answer 1

The correct option is B A carbanion $(-\stackrel{-}{C}{H}_2)$

Hyperconjugation :
It is a stabilising effect due to the reason that octet of carbon is always complete. Stability is also increased due to the delocalisation of sigma-pi electrons.

Condition for hyperconjugation :
Atleast one $\alpha$ hydrogen has to be present.

Hyperconjugation is mainly observed in:
1. A free radical $(-\stackrel{\bullet }{C}{H}_2)$
2. A carbocation $(-\stackrel{+}{C}{H}_2)$
3. A double bond $\text{>C=C<}$
It is not observed in carbanion because of its fully filled p-orbital (or octet).