Explain why alky1 groups act as electron donors when attacted to a `pi-system`.

Explanation

Alkyl is an electron-releasing group. It acts as an electron-donar species. The carbocations in which carbon atom has sextet configuration (and hence electron deficient) can receive a pair of electrons from the alkyl halide. In alkyl halide, the polarity of bond `(C - X)` has partical positive charge on carbon atom and hence the carbon atom becomes and electrophile centre at which a nucleophile can attack. Moreover, when alkyl group is attached to `pi-system` like in ethanol due to greater `EN` of `O` than `C,pi overline e^, s` are withdrawn by oxygen through electromeric effect and `C-1` aquires a positive change and oxygen atom acquires a negative charge . So to overcome the deficiency of `overline e` on `C-1, (CH_3)` group attached to it gives `sigma overline e^, s` to `C-1` and thus `(CH_3)` group acts as an `overline e` donar via inductive effect.
This can also be explained by hyperconjugation, e.g.,
.