The hyperconjugative stabilities of tert-butyl cation and 2-butene, respectively, due to

1. $\sigma \to \text{p}(empty) and \sigma \to {\pi }^{*}electron\; delocalisations.$
2. $\sigma \to {\sigma }^{*}and\sigma \to \pi electron\; delocalisations.$
3. $\sigma \to \text{p}(filled) and \sigma \to \pi electron\; delocalisations.$
4. $\text{p (filled)}\to {\sigma }^{*}and\sigma \to {\pi }^{*}electron\; delocalisations.$

Solution

 
In tert-butyl cation, carbon bearing $\oplus$ charge has one vacant p orbital hence it is $\text{σ}-\text{p}$ (empty) conjugation or Hyperconjugation.
 
In 2-butene hyperconjugation between ​$\text{σ}$ and ${\text{π}}^{*}$ bond.

Asked in: JEE Advanced 2013 (Paper 1)

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