Alkenes and Peracids
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What is a peracid?
R-COOOH C=O C-O O-OH
What product is formed when you react an alkene with a peracid?
epoxide
Where on a peracid is the nucleophile likely to attack and why?
The oxygen on the OH The O-O bond is very weak and it breaks the weakest bond
What is the most commonly used peracid? Draw its structure.
mCPBA
What is a negative about mCPBA?
It is very reactive and explosive at high amounts/concentrations All products are organic, hard to seperate byproduct from the desired product
How many mechanistic steps does the formation of the peracid using mCPBA occur in?
1
What type of reaction is peracid formation?
Synaddition
What happens during a peracid formation reaction?
The charge is delocalised to make it more stable Both c-o bonds are formed at the same time
If the alkene is cis, what will the epoxide be?
Cis
If the alkene is trans, what will the epoxide be?
Trans
How is the formation of epoxides stereospecific?
Each diastereomer of an alkene gives a different diastereomer of the epoxide product
What type of reaction do epoxides go to open the ring?
Sn2 reaction with nucleophiles
Overall, what does the epoxide ring opening result in?
Anti-addition of OH and the nucleophile
Can epoxides ring open by both SN1 and SN2? Draw the mechanism
Yes
What type of reaction will the alkene undergo if it is unsymmetrical?
SN2
Where will the nucleophile attack in the SN2 reaction?
The least hindered end of the epoxide
What happens when epoxides react with nucleophiles in SN1 conditions?
The nucleophile will add to whichever end of the epoxide is best able to stabilise a positive charge
What conditions are needed for SN1?
Acid catalyst