Question

The hyperconjugative stabilities of tert-butyl cation and 2-butene, 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 \pi(filled) \, and \, \sigma \rightarrow \pi $ electron delocalisations
• D. $\pi (filled) \rightarrow \sigma ^* \, and \, \sigma \rightarrow \pi ^* $ electrons delocalisations

Answer 1

The Correct Option is A

PLAN Spreading out charge by the overlap of an empty p-orbital with
an adjacent $\sigma - $ t-bond is called hyperconjugation. This overlap
(the hyperconjugation) delocalises the positive charge on the
carbocation, spreading it over a larger volume, and this
stabilises the carbocation.
tertiary butyl carbocation has one vacant p-orbital, hence, it is
stabilised by $\sigma - p $ (empty) hyperconjugation.
In 2-butene, stabilisation is due to hyperconjugation between
$\sigma - \pi ^* $ electron delocalisation.