Chapter 15: Alcohols, Diols and Thiols

Hydration of Alkenes
(review of Chapter 6)

Summary

• When treated with aq. acid, most commonly H₂SO₄,  alkenes form alcohols.
• Regioselectivity predicted by Markovnikov's rule
• Reaction proceeds via protonation to give the more stable carbocation intermediate.
• Not stereoselective since reactions proceeds via planar carbocation.

• Hydroboration-Oxidation
• Oxymercuration-Demercuration

MECHANISM FOR REACTION OF ALKENES WITH H3O+
Step 1: An acid / base reaction. Protonation of the alkene to generate the more stable carbocation.  The p electrons act pairs as a Lewis base.
Step 2: Attack of the nucleophilic water molecule on the electrophilic carbocation creates an oxonium ion.
Step 3: An acid / base reaction. Deprotonation by a base generates the alcohol and regenerates the acid catalyst.

© Dr. Ian Hunt, Department of Chemistry