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

Options

A. `sigma to pi` (empty and `sigma to pi^(**)` electron delocalizations
B. `sigma to sigma^(**) and sigma t o pi` electron delocalizations
C. `sigma to pi` (filled) and `simga to pi` electron delocalizations
D. `pi`(filled) `to sigma^(**) and sigmato pi^(**)` electron delocalizations

Answer

A

Explanation

In tert-butyl cation, the carbon bearing positive charge has an empty p-orbital and hence hyperconjugation here involves o-p(empty) electron delocalisation.

In 2-butene, `pi`- bond contains two electrons, one electron from each of the two carbon atoms, ie, `pi = MO` contains a pair of electrons, but `pi^(**) MO` is empty and hence electrons of the `sigma C - H` bond can move only into the `pi^(**)` orbital.