The interaction of a functional group with sigma bonds with the pi bonds in conjugated molecules, causing the functional group to act as an additional conjugation in the molecule. The interaction of a methyl group with the benzene ring in methylbenzene (toluene) is a notable example. Hyperconjugation has been postulated to explain the stability of certain entities in organic chemistry and certain effects in stereochemistry. It can be explained in terms of either molecular-orbital theory or resonance structures in valence-bond theory.