Hyperkonjugerende

Hyperkonjugering, often referred to in English as hyperconjugation, is a stabilizing interaction in organic chemistry in which electrons in a σ-bond adjacent to an unsaturated center delocalize into an empty p orbital or into a π-system. The phenomenon is commonly described using σ bonds from C–H or C–C bonds that lie next to a carbocation, a radical, or a π-bond, leading to a partial sharing of electron density with the unsaturated site.

Mechanistically, hyperkonjugerende involves overlap between a filled σ orbital and an adjacent empty p orbital or π-system. This interaction lowers the overall energy of the system and provides a qualitative explanation for certain stability trends. It is distinct from conjugation in that it centers on σ bonds interacting with an unsaturated center rather than direct π–π overlap, though the effects can be complementary.

In carbocations, hyperkonjugering is a major factor in stabilization. The number of hyperconjugative structures corresponds to the β C–H and C–C bonds on neighboring carbons; tertiary carbocations have more such bonds and are therefore more stable than primary or secondary ones. In alkenes, hyperkonjugering from σ bonds on alkyl substituents adjacent to the double bond also stabilizes the π-system, contributing to the observed trend that more substituted alkenes are generally more stable and exhibit lower heats of hydrogenation.

Hyperkonjugerende effects extend to radicals and benzylic or allylic systems, where σ-bond donation helps delocalize electron density. While useful as a model for explaining stability trends, hyperkonjugation is a qualitative concept, not a discrete resonance structure.