Epoxidation: practice and mechanism
The peracid transfers exactly one oxygen atom to the double bond: a three-membered ring (epoxide) forms, no OH groups.
Example
The peracid (meta-chloroperbenzoic acid) transfers one oxygen atom to the double bond in a single step. An epoxide (three-membered ring with oxygen) forms.
Mechanism step by step
- 1
The terminal oxygen of the peracid is electrophilic.
- 2
In a single step ("butterfly" transition state) this oxygen is transferred to the double bond.
- 3
The epoxide and meta-chlorobenzoic acid form; the alkene geometry is preserved.
Practice tasks
Which product forms, which reagent is needed? After each answer you see the explanation.
Which main product forms?
Typical mistakes
Often confused with: syn dihydroxylation · Ozonolysis (reductive work-up)
Frequently asked questions
What are epoxides used for?
Ring strain makes them reactive: acid/water gives trans diols, nucleophiles give ring-opened products.
What is the difference to OsO₄?
mCPBA gives an epoxide (one O). OsO₄ gives a cis diol directly (two OH).