Question

Explain why alkyl groups act as electron donors when attached to a $\pi$ system.

Answer 1

Due to hyperconjugation, the alkyl groups act as electron donors when attached to a π system. Due to hyperconjugation, the pi electrons are delocalized. The delocalization is due to partial overlap of $s{p}^3-s$ sigma bond orbital with an empty p orbital of the pi bond of adjacent C atom. This increases the stability of molecule.