Hyperconjugation
The stabilising delocalisation of electrons from a sigma C–H bond into an adjacent empty or partly filled p orbital.
Unit
kJ/mol
In depth
Sometimes called no-bond resonance, hyperconjugation increases with the number of alpha hydrogens available. It is the principal reason tertiary carbocations and more highly substituted alkenes are the more stable, which in turn underlies Markovnikov's and Zaitsev's rules.
Examples in the real world
The tert-butyl cation gaining stabilisation from nine alpha hydrogens; 2-methylbut-2-ene being the most stable C₅H₁₀ alkene.