Final answer:
The correct intermediate for the hydration of alkenes is a carbocation. Water acts as a nucleophile and attacks this intermediate, eventually forming an alcohol. Sulfuric acid is a common catalyst in this reaction.
Step-by-step explanation:
In the hydration of alkenes, the intermediate that is thought to occur in the presence of acid is not a free radical or an alkyne. Instead, the process involves the formation of a carbocation intermediate. In the first step of the mechanism, the alkene is protonated by the acid, resulting in a carbocation. This is followed by water acting as a nucleophile in the second step, where it attacks the carbocation, leading to the formation of an alcohol once the excess proton is removed by another water molecule.
Therefore, the correct intermediate for the hydration of alkenes is the carbocation, not a free radical or alkyne. Sulfuric acid (H2SO4) is often used as the acid catalyst in this reaction because its conjugate base, HSO4-, is a poor nucleophile, which promotes the reaction of water with the carbocation over reversion to the alkene. In addition, the hydration reaction is important for the synthesis of alcohols from alkenes.