The interaction of sigma bonds with pi bonds in a molecule, as in the interaction of a methyl group with the benzene ring in toluene. It is postulated to account for the stability of some carbonium ions. Hyperconjugation is often thought of as a contribution of resonance structures in which a sigma bond is broken to give ions; e.g. C6H5CH2−H+ in toluene. It has been called no-bond resonance.