Hyperconjugation is a general stabilising interaction. It involves delocalisation of sigma electrons of C-H bond of an alkyl group directly attached to an atom of unsaturated system or to an atom with an unshared p-orbital. The sigma electrons of C-H bond of the alkyl group enter into partial conjugation with the attached unsaturated system or with the unshared p-orbital. Hyperconjugation is a permanent effect. An alkyl group is a functional group which replaces one of the hydrogen atoms in the structure of the hydrocarbon. Actually, it itself is a hydrogen with one hydrogen atom less. Example- methyl group CH3, Ethyl group C2H5 etc.