hyperkonjugationsstabiliserade

Hyperconjugation is a stabilization mechanism in organic chemistry in which sigma bonds adjacent to an unsaturated center delocalize electron density into an empty orbital or into a pi system. This interaction can occur with sigma bonds involving C–H or C–C bonds that lie next to a positively charged carbon, a radical, or a double bond.

In carbocations, hyperconjugation involves donation of electron density from neighboring C–H (or C–C) sigma bonds into the empty p orbital on the cationic center. Each neighboring sigma bond can be viewed as contributing a hyperconjugative structure; for example, the tert-butyl cation (C(CH3)3+) has nine such structures, reflecting nine adjacent C–H bonds.

In alkenes, hyperconjugation stabilizes the double bond and influences reactivity and thermochemistry. More substituted alkenes have more hyperconjugative interactions, leading to greater stability: mono-substituted < di-substituted < tri-substituted alkenes. Hyperconjugation also contributes to the stabilization of alkyl radicals through adjacent C–H sigma bonds.

Hyperconjugation is a form of delocalization sometimes described as no-bond resonance. It complements classical resonance by accounting for stabilization arising from sigma–orbital interactions and by explaining how alkyl groups affect stability and reactivity. The effect depends on orbital overlap and geometry, and while it provides a useful approximation, it is not a discrete chemical bond.