Define hyper conjugation ?

Hyperconjugation effect: It is an extension of resonance effect, as it involves delocalization of sigma electrons of C-H bond of an alkyl group directly attached to an atom of unsaturated system or an atom with an unshared p orbital.

The inductive effect of alkyl group is reversed when attached to an unsaturated system such as double bonds or benzene rings. This change in the behaviour is called as hyperconjugation effect.

The order of I- effect in alkyl gr. of a saturated system is ; (CH₃)₃ C-> (CH₃)₂ CH- > CH₃CH₂- > CH₃ -

This order is reversed in unsaturated system due to hyperconjugation effect. The effect works as;

Here structure 1, 2 and 3 are called as hyperconjugative structures.

It is also shown that, the hyperconjugation depends on no. of alfa H atoms, and so as much is the hydrogen atoms that much will be the hyperconjugative structures.