Carbocations
118.3 Formation of Carbocations
Carbocation intermediates are formed in three main types of reactions: additions to pi
bonds, unimolecular eliminations, and unimolecular nucleophilic substitution. On a bridge
head a positive carbon is rare. The 3-cyclopropyl carbocation is the most stable carbocation.
118.4 Reactions of Carbocations.
In general, carbocations will undergo three basic types of reactions:
118.4.1 1. Nucleophile Capture
Carbocations will react with even mild nucleophiles (such as water) to form a new bond.and
formation of carbon free radical
118.4.2 2. Elimination to form a pi bond
Carbons alpha to the carbocation will often lose a proton to form a double (or, in some
cases) triple bond from the carbocation. Such a reaction requires only a mild base (e.g.
chloride) to remove the proton.
118.4.3 3. Rearrangement
A secondary carbocation may rearrange to form a tertiary carbocation before the ion is
stabilized using one of the above-mentioned reactions. Since a cation constitutes a deficiency
of electrons, the empty orbitals do not move; rather, a hydrogen atom bonded to a nearby
carbon is moved to stabilize the secondary carbocation, of the hydrogen atom creates a
new tertiary carbocation, which is more stable and will be substituted to lead to the final
product. See w:carbocation rearrangement^1.