Carbocation rearrangement is a process in which the carbocation intermediate can form a more stable ion. With carbocation rearrangement, the reaction would not be able to hydrate quickly under mild conditions and be produced in high yields. This reaction is very fast and proceeds with 90% yield.

This reaction involves a mercury acting as a reagent attacking the alkene double bond to form a mercurinium ion Bridge. A water molecule will then attack the most substituted carbon to open the mercurium ion bridge, followed by proton transfer to solvent water molecule.

The organomercury intermediate is then reduced by sodium borohydride – the mechanism for this final step is beyond the scope of our discussion here. Notice that overall, the oxymercuration – demercuration mechanism follows Markovnikov’s regioselectivity with the OH group is attached to the more substituted carbon and the H is attach to the less substituted carbon. The reaction is useful, however, because strong acids are not required, and carbocation rearrangements are avoided because no discreet carbocation intermediate forms.  However, it does require the use of highly toxic mercury compounds.