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Concept
Oxymercuration reaction
Résumé
In organic chemistry, the oxymercuration reaction is an electrophilic addition reaction that transforms an alkene () into a neutral alcohol. In oxymercuration, the alkene reacts with mercuric acetate () in aqueous solution to yield the addition of an acetoxymercury () group and a hydroxy () group across the double bond. Carbocations are not formed in this process and thus rearrangements are not observed. The reaction follows Markovnikov's rule (the hydroxy group will always be added to the more substituted carbon) and it is an anti addition (the two groups will be trans to each other).
Oxymercuration followed by reductive demercuration is called an oxymercuration–reduction reaction or oxymercuration–demercuration reaction. This reaction, which is almost always done in practice instead of oxymercuration, is treated at the conclusion of the article.
Oxymercuration can be fully described in three steps (the whole process is sometimes called deoxymercuration), which is illustrated in stepwise fashion to the right. In the first step, the nucleophilic double bond attacks the mercury ion, ejecting an acetoxy group. The electron pair on the mercury ion in turn attacks a carbon on the double bond, forming a mercuronium ion in which the mercury atom bears a positive charge. The electrons in the highest occupied molecular orbital of the double bond are donated to mercury's empty 6s orbital and the electrons in mercury's dxz (or dyz) orbital are donated in the lowest unoccupied molecular orbital of the double bond.
In the second step, the nucleophilic water molecule attacks the more substituted carbon, liberating the electrons participating in its bond with mercury. The electrons collapse to the mercury ion and neutralizes it. The oxygen in the water molecule now bears a positive charge.
In the third step, the negatively charged acetoxy ion that was expelled in the first step attacks a hydrogen of the water group, forming the waste product HOAc.
Source officielle
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