Question

The triphenylmethyl cation is so stable that some of its salts can be stored for months. Explain why this cation is so stable.

triphenylmethyl cation

Short answer

The triphenylmethyl cation is extremely stable because it has three phenyl groups to stabilize the positive charge. The positive charge on carbon is in conjugation with three phenyl groups which make this carbocation more stable.

Step-by-step solution

Carbocation definition

A carbocation is a species that contains a carbon atom bearing a positive charge. The positively charged carbon atom is bonded to three other atoms, and it has no nonbonding electrons, so it has only six electrons in its valence shell.

Stability order of carbocation

The order of stability is

tertiary carbocation (most stable) >secondary carbocation>primary carbocation (least stable).

Step 3: Stability of triphenylmethyl cation

Here in triphenylmethyl cation, positive charge is on C-atom which is next to benzene (phenyl group) ring. This phenyl group helps in the delocalization of positive charge in the ring which makes them stable carbocation. Also there are three phenyl group which make further stable this triphenylmethyl carbocation.