The anomeric effect is sometimes considered the negative version of this effect.
The adamantyl ion provides some of the only structural evidence for this phenomenon. Bridgehead-substituted bicyclic halides have been used to explore the relative effects of this phenomenon and the inductive effect. A silyl substituent greatly enhances ionization of the carbon atom beta to it through this mechanism. The anomeric effect is sometimes considered the negative version of this effect. This effect explains why the carbon-carbon single bond in propene is shorter than the carbon-carbon single bond in ethane; in propene the bond takes on some double-bond character through this mechanism. It is the principal mechanism for the stabilization of carbocations by alkyl substituents. For 10 points, name this chemical effect in which electrons from a filled carbon-carbon or carbon-hydrogen bonding orbital are donated to a nonbonding p orbital.
The adamantyl ion provides some of the only structural evidence for this phenomenon.
hyperconjugation [accept word forms, don't accept conjugation. accept no-bond resonance, prompt on resonance]