Carbocation definition
Carbocation is the intermediate
of carbon containing positive charge. It has six electrons in the valence
shell.
Carbocation formation
Carbocation is formed by the heterolytic bond fission between C-X in an organic
compound.If X is more electronegative than carbon , the former takes away the
bonding electron pair and becomes negatively charged. And carbon becomes
positively charged (carbocation).
Carbocation hybridization
Hybridization of C+ = sp2
Geometry
of C+ =
Trigonal Planar
Carbocation stability order:
There are three factors contributing to the stability of carbocations:
(a) Inductive
Effect
(b) Hyperconjugation
(c) Resonance
(b) Hyperconjugation
(c) Resonance
(a) Inductive Effect: The carbocation is stabilized by ERG and
destabilized by EWG.
(b) Hyperconjugation: The positive
charge is delocalized over α-H
atoms and the octet of the C carrying positive charge is completed.
(c) Resonance: Resonance is a stabilizing factor as it
delocalizes the positive charge and therefore provides stability.
Both these carbocations are
very highly stable due to resonance.
Both vunyl and phenyl carbocations are highly unstable. resonance is absent as there is no conjugation between pie electrons and positive charge.
Orbital Picture of Vinyl Carbocation :
The empty ‘p’ orbital is
perpendicular to the ‘p’ orbitals forming the p bond.
Orbital Picture of Phenyl Carbocation
