Question

The hyperconjugative stabilities of tertiary − butyl carbocation and but-2−ene, respectively, are due to

• A. $\sigma \rightarrow p$ (empty) and $\sigma \rightarrow \pi *$ electron delocalisations.
• B. $\sigma \rightarrow \sigma *$ and $\sigma \rightarrow \pi $ electron delocalisations.
• C. $\sigma \rightarrow p$ (filled) and $\sigma \rightarrow \pi $ electron delocalisations.
• D. $p$ (filled) $ \rightarrow \sigma *$ and $\sigma \rightarrow \pi *$ electron delocalisations.

Answer 1

Answer: (A)

Hyperconjugation effect is a permanent effect in which localization of σ electrons of C-H bond of an alkyl group directly attached to an atom of the unsaturated system or to an atom with an unshared p orbital takes place. It increases stability of carbocation, free radical and alkenes by decreasing energy.

$CH _{3}- CH _{2}- CH = CH _{2}(\sigma-\pi *$ electron $)$ del ocalization.