Question

What are carbocations ? Discuss their various types.

Answer 1

A carbocation is a molecule in which a carbon atom has a positive charge and three bonds. We can basically say that they are carbon cations. Formerly, it was known as carbonium ion. Carbocation today is defined as any even-electron cation that possesses a significant positive charge on the carbon atom.

The different carbocations are named on the basis of the number of carbon groups bonded to the carbon. The carbocation can be termed as methyl, primary, secondary or tertiary on the basis of how many carbon atoms are attached to it:

i) Methyl carbocation: If no carbon is attached to the carbon with the positive charge it is simply called as methyl carbocation.

ii) If one, two or three carbon is attached to the carbon with the positive charge it is called the primary carbocation, secondary carbocation, tertiary carbocation respectively.

iii) If there is a carbon-carbon double bond next to the carbon with the positive charge it is termed as allylic carbocation.

iv) In the same way, if the carbon with the positive charge is attached to a double bond, the carbocation is termed as vinylic carbocation. Here, hybridization of the carbon having the positive charge is sp and geometry is linear.

v) Whenever the carbon which consists of the positive charge is part of a benzene ring, then the carbocation an aryl carbocation.

vi) If the carbon having a positive charge is immediately next to a benzene ring, it is termed as a benzylic carbocation.