Step 1: Formation of the Carbocation Intermediate

The leaving group (such as OTs⁻) departs from the substrate molecule. This results in the formation of a tertiary carbocation, where the positively charged carbon is bonded to three alkyl groups.

Tertiary carbocations are highly stabilized due to inductive effects and hyperconjugation from surrounding alkyl groups.

Step 2: Nucleophilic Attack

The nucleophile (e.g., CH₃OH) attacks the positively charged carbon atom (the carbocation). This leads to the formation of an oxonium ion intermediate (a positively charged oxygen species).

In this oxonium ion, the oxygen atom carries a positive charge because it forms three bonds — two with carbon and one with hydrogen.

Step 3: Deprotonation

A base present in the medium abstracts a proton (H⁺) from the oxonium ion. This neutralizes the oxygen and forms the final ether product.

This step restores a lone pair to the oxygen atom, completing the substitution reaction.

Final Summary

• Reaction proceeds via a unimolecular substitution (SN1) mechanism.
• Key steps: formation of carbocation → nucleophilic attack → deprotonation.
• Favoured by tertiary carbocations and polar protic solvents.