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Oxymercuration is a special electrophilic addition. It is anti-stereospecific and regioselective. Regioselectivity is a process in which the substituents choses one direction it prefers to be attached to over all the other possible directions. The good thing about this reaction is that there are no carbocation rearrangement due to stabilization of the reactive intermediate. Similar stabilization is also seen in bromination addition to alkenes.
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. A temporary secondary carbocation will be formed after the double bond attacks the mercury but the pair of electrons on the mercury will soon attack the carbon with the secondary carbocation to create a Mercurinium Ion Bridge. A water molecule will then attack the most substituted carbon. The most substituted carbon is the carbon that is attached to the most number of carbons. After the water molecule attacks the more substituted carbon, the Mercurinium Ion bridge then opens up. After the Mercuriunium Ion opens up, another water molecule will depronate the hydrogen of the first water molecule that was attached to the more substituted carbon leaving an OH group attached to that carbon. This explains the end of Oxymercuration.
As for Demercuration, it is the process which involves the removal of mercury using Sodium Hydroboride. One of the hydrogens (a hydride) of Borohydride will do a backside displacement (SN2 type reaction) on the least substituted carbon kicking off the mercury. Both Oxymercuration - Demercuration Mechanism follows Markovnikov's Regioselectivity. Markovnikov's Regioselectivity is the process in which the OH group is attached to the most substituted carbon and the H is attach to the least substituted carbon. This process can also be viewed in the animation I created below. Below is a step by step tutorial of when the process of the mechanism. I also added a nice instrumental song so the viewers would not get bored.
What are the end products of these reactants?
The end product to these practice problems are pretty much very similar. First, you locate where the double bond is on the reactant side. Then, you look at what substituents are attached to each side of the double bond and add the OH group to the more substituent side and the hydrogen on the less substituent side.
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