Carbonium ion


source : difference

Carbonium ion or carbocation-

When a covalent bond, in which Carbon  is linked to more electronegative atom or group, breaks up by heterolytic fission . The more electronegative atom takes away the electron pair while carbon loses its electron & thus carbon acquires a positive charge .  These are obtained by heterolytic fission.


“Such organic ions carrying a positive charge on Carbon-atom are known as Carbonium ion or Carbocations.”

These are named by adding the ‘Carbonium ion’ after the name of parent alkyl group . There are also termed as Primary , secondary  & tertiary  depending upon the nature of Carbon-atom bearing positive charge .


Characteristics :

1)  Carbon-atom of the carbonium ion contains positive charge.

2) Carbon-atom carrying positive charge has six electrons in its valence shell i.e., two electrons less than octet.

3) The positively charged carbon-atom of  carbonium ion  is in sp2 hybridization state. Its shape is planar. It uses sp2 hybrid orbitals to form  three sigma  bonds .

4) These  are very reactive. They readily react with the groups which can donate a pair of electron . (example – nucleophiles)


5) Carbocation is itself an electrophile

6) The order of stability of carbonium ions are as follows-


7) The presence of a group  having -I effect such as (-Cl) decreases the stability & increases the reactivity.

On the other hand, the presence of a  group  having +I effect , in a carbocation  increases stability and decreases its reactivity.


8)The stability of a carbocation is influenced by resonance. Both allyl & benzyl carbonium ions possess resonance & thus extra stable.