The methyl group does not possess an unshared pair of electrons. But F.A. Matsen has introduced the concept of the methyl group as a Pseudo-heteroatom which contributes a pair of electrons to ${pi}$ system. In this heteroatom model, A. Streitwieser et al have assumed that the electrons in a methyl group behave to their approximation as a single electron pair on a single atom. But the theoretical basis on the heteroatom model hyper-conjugation has not studied yet. In this paper, Linear combination of Bond orbital and group theory is used to investigate the theoretical basis for it.