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ChemWiki: The Dynamic Chemistry E-textbook > Organic Chemistry > UMM chemwiki project > Alkenes and alkynes > Reactions of alkenes-an overview > Oxymercuration-Demercuration: A Special Electrophilic Addition

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Oxymercuration-Demercuration: A Special Electrophilic Addition

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.

Introduction

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.

Oxymercuration / Demercuration

                             Oxymercuration - Demercuration Rxn (1).bmp
       Oxymercuration - Demercuration Mechanism (2).bmp

Oxymercuration / Demercuration Mechanism

In this animation, I included 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. The video is kind of glitchy but it is still readable. I edit the video and made the animation slower. All my explanation are pretty much in this animation because I think pictures explains more than words. By the way, this animation is original. I created it myself, not copyrighted.

Another new version: the glitchy-ness decrease but it's still there. It's just not as much as before.

Get Adobe Flash player

References

  1. Vollhardt, K. Peter C. Organic chemistry structure and function. New York: W.H. Freeman, 2007.                                  
  2. Smith, Michael B., and Jerry March. March's Advanced Organic Chemistry Reactions, Mechanisms, and Structure (March's Advanced Organic Chemistry). New York: Wiley-Interscience, 2007.                                                                                                                                                             
  3. Narasimhan, Calamur, Martin E. Carrera, and Richard A. Wilsak. "Butylenes." Kirk‑Othmer Encyclopedia of Chemical Technology. 15 Aug. 2003. 4 Mar.  <http://mrw.interscience.wiley.com/em...oxymercuration>                                                                                                         

Some Practice Problems

What are the end products of these reactants?

Practice Problems (1).bmp

Answers
Answers (1).bmp

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.

Contributors

  • Duyen Dao-Tran

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Last Modified
20:49, 3 Aug 2014

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