Hyperconjugation is a concept in organic chemistry that refers to the delocalization of electrons with the participation of bonds of primarily σ-character. It involves the interaction of the electrons in a sigma (σ) orbital (e.g. C–H or C–C) with an adjacent unpopulated non-bonding p or antibonding σ* or π* orbitals to give a pair of extended molecular orbitals. This interaction increases the stability of the system by increasing electron delocalization.

Hyperconjugation can be used to explain a variety of chemical phenomena, including the anomeric effect, the gauche effect, the rotational barrier of ethane, the beta-silicon effect, the vibrational frequency of exocyclic carbonyl groups, and the relative stability of substituted carbocations and substituted carbon-centered radicals. It is also a factor in explaining why increasing the number of alkyl substituents on a carbocation or radical center leads to an increase in stability.

In summary, hyperconjugation is a concept in organic chemistry that explains the delocalization of electrons with the participation of bonds of primarily σ-character, which increases the stability of the system. It can be used to explain various chemical phenomena and is a factor in explaining the increased stability of carbocations and radicals with increasing alkyl substituents.