Hydration of Alkenes:

Hydration of Alkenes:

• this reaction is the addition of water to a molecule with a double bond  ,another kind of electrophilic addition reaction is called hydration. As the name suggests,
• Hydration requires the presence of a strong acid catalyst.
• ( A catalyst is a substance that accelarates a reaction, but is not actually consumed in the reaction).
• Similar to  the addition of hydrogen halides to alkenes, the addition of water is regioselective .
• The first step is the attack of the electrons of the pi bond on a proton (usually shown on a hydronium ion).
•  In the next step of the reaction, a lone pair of electrons from the oxygen of water attack the carbocation to give another intermediate which bears a positive charge on oxygen, this is called an oxonium ion
• In the final step of the reaction, a proton is removed from the oxygen by water to regenerate the hydronium ion, and to give the alcohol product.
• Rearrangements are possible here as well
• Water, itself, is too weak an acid to transfer the proton to the alkene, so acid catalysis is essentialNote also that the product is an alcohol.
• Note that the Markovnikov Rule is followed for this reaction, i.e., the proton adds to the less substituted carbon of the alkene double bond (the methylene carbon, making it a methyl group), and the hydroxyl group adds to the more highly substituted carbon atom of the alkene double bond. So the regiochemistry of the hydration reaction is closely parallel to that previously discussed for the hydrochlorination reaction.

example  with rearrangement and ring expansion.