The delocalization of σ-electrons or lone pair of electrons into adjacent π-orbital or p-orbital is called hyperconjugation. It is also known as no bond resonance as there is no bond between the α-carbon atom and one of the hydrogen atoms.
Hyperconjugation
It is a permanent effect and its effect is stronger than the inductive effect because, in Inductive effect there is partial delocalization of charges, but in Hyperconjugation there is total transfer or delocalization of charge.
It occurs due to overlapping of σ-bonding orbital or the orbital containing a lone pair with adjacent π-orbital or p-orbital.
For a molecule to show hyperconjugation, there must be an α-C-H group or a lone pair on atom adjacent to sp2 hybrid carbon or other atoms like nitrogen, oxygen etc. Greater the number of hyperconjugative structure , greater would be the stability of the molecule.
Alkenes, alkyl carbocations, alkyl free radicals, nitro compounds with α- hydrogen shows hyperconjugation.
hyperconjugation Although a free proton has been shown in the above structures, it is still bound quite firmly to the p-cloud, and hence it is not free to move.