Question

The acid-catalyzed hydration of 3,3 -dimethyl-1-butene gives 2,3 -dimethyl2 -butanol as the major product. Propose a mechanism for the formation of this alcohol.

Short answer

Question: Describe the mechanism for the acid-catalyzed hydration of 3,3-dimethyl-1-butene to form 2,3-dimethyl-2-butanol. Answer: The mechanism for this reaction consists of three main steps: 1. Protonation of the double bond, forming a tertiary carbocation; 2. Nucleophilic attack by water, resulting in the formation of an oxonium ion; 3. Deprotonation of the oxonium ion to form the alcohol product, 2,3-dimethyl-2-butanol.

Step-by-step solution

Protonation of the double bond

The acid catalyst, H+, donates a proton to the carbon-carbon double bond (C=C) of 3,3-dimethyl-1-butene. This protonation step forms a more stable carbocation intermediate. The more substituted carbon in the double bond will bear the positive charge due to more effective electron delocalization, i.e., 3° carbocation is more stable than 2°. The resulting structure will be a tertiary carbocation.

Nucleophilic attack by water

A water molecule, which acts as a nucleophile, attacks the positively charged carbon of the carbocation. This nucleophilic attack results in the formation of an oxonium ion, where the oxygen atom of the water molecule is now bonded to the carbon and carries a positive charge.

Deprotonation to form the alcohol

The oxonium ion undergoes deprotonation, losing a proton to form the desired alcohol product. Another water molecule or a base can act as the deprotonating agent, taking the proton from the oxonium ion to form 2,3-dimethyl-2-butanol. This step completes the mechanism for the acid-catalyzed hydration of 3,3-dimethyl-1-butene.