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Hyperconjugation is a type of chemical bonding interaction that involves the delocalization of electrons from a sigma bond (usually C-H or C-C) into an adjacent empty or partially filled p-orbital or pi-system. This interaction is most commonly observed in organic molecules and is responsible for stabilizing certain structures.

The effect is most pronounced when the sigma bond is in a favorable orientation relative to the acceptor orbital. For instance, in carbocations, hyperconjugation occurs between the filled C-H sigma bonds and the empty p-orbital of the positively charged carbon atom. This delocalization of electron density effectively spreads out the positive charge, making the carbocation more stable. Similarly, hyperconjugation can stabilize carbanions and free radicals by delocalizing the negative charge or unpaired electron into adjacent sigma bonds.

Hyperconjugation also plays a role in the stability of alkenes. The C-C sigma bond of the alkene system can interact with the adjacent pi system, leading to increased stability. The more alkyl substituents an alkene has, the greater the extent of hyperconjugation, and thus the greater its stability. This principle is often used to explain the relative reactivity and stability of different alkene isomers. While often discussed in terms of sigma-pi interactions, hyperconjugation can also involve sigma-sigma interactions, though this is generally a weaker effect. The overall concept is the delocalization of electron density from filled sigma orbitals into adjacent low-lying unoccupied orbitals.