Is acid-catalyzed hydration stereoselective?

1 Answer
Dec 9, 2014

Acid-catalyzed hydration of alkenes is not stereoselective.

The steps in the mechanism are:

  1. Protonation of the π bond to form a carbocation
  2. Addition of water to the carbocation to form an oxonium ion
  3. Deprotonation of the oxonium ion to form an alcohol.

This carbocation formed in Step 1 is #sp^2# hybridized. It is planar, so it can react with a water molecule on either the top or the bottom face.

That means that the reaction is not stereoselective.

If the carbon bearing the OH group is chiral, we get a mixture of (R) and (S) alcohols.