||Organic Chemistry 4e Carey||
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Chapter 14: Organometallic Compounds
Overview of Reactions |
Overview of Grignard Reactions |
Addition of RLi and RMgX to Aldehydes and Ketones |
Addition of RCCM to Aldehydes and Ketones |
Addition of RLi and RMgX to Esters |
Alkane synthesis using R2CuLi |
Reactions of RZnX |
Oxymercuration-Demercuration of Alkenes |
Reaction type: Electrophilic
- Overall transformation
C=C to H-C-C-OH
- This is an alternative
method for hydrating alkenes to give alcohols
- Typical reagents are
mercury acetate, Hg(OAc)2 in aqueous THF
- Unfortunately, mercury
compounds are generally quite toxic
- Regioselectivity predicted
by Markovnikov's rule
(most highly substituted alcohol)
- The reaction is not
- Reaction proceeds via
the formation of a cyclic mercurinium ion (compare with bromination
- The mercurinium ion
is opened by the attack of water to complete the oxymercuration.
- When the water attacks,
it does so at the more highly substituted carbon.
is effected by a reduction using sodium borohydride, NaBH4
- If the reaction is carried
out in the presence of an alcohol rather than water, then ethers are obtained.
- What other methods are
there for hydrating alkenes ?
- Which species in this
reaction is/are organometallic species ?
- Why aren't rearrangements
a problem with this process ?
- Why does the water attack
the more highly substituted carbon ?
REACTION OF ALKENES WITH Hg(OAc)2 / H2O
The p electrons act as the nucleophile with
the electrophilic Hg and loss of an acetate ion as a leaving group, forming
the mercurinium ion.
Water functions as a nucleophile and attacks one of the mercury substituted
carbons resulting in cleavage of the C-Hg bond.
The acetate ion functions as a base deprotonating the oxonium ion to give
the alcohol. This completes the oxymercuration part of the reaction.
4:(mechanism not shown)
The hydride reduces the Hg off, creating a C-H bond while breaking the
C-Hg bond. This is the demercuration part of the process.