Epoxide opening under base
With no acid to open the ring first, the nucleophile has to attack it directly, so it goes to the carbon that is easier to reach — the less substituted one.
What it needs, and what it gives
- Reaction class
- Substitution
- An alkoxide or hydroxide. Addition is anti across the old ring.
- balanced — the co-products are written out, not dropped
- Mechanism
- Epoxide opening under base, 3 steps
How it is thought to happen
A base makes the nucleophile, the nucleophile attacks the less crowded end of the ring, and the strained ring springs open.
- The base makes the nucleophile
- The alkoxide attacks the less crowded carbon
- The alkoxide takes a proton
Try it on your own structures
Enter your reactants in the Reaction Lab. If this transformation matches what you drew, it is applied and the outcome is shown next to the records that back it — with the count of documented reactions doing the same thing on substrates like yours, rather than a confidence score.
Other substitution transformations
Substitution by an anionic nucleophile
An anion displaces the halide from the back, turning the carbon over.
Epoxide opening under acid
An acid protonates the epoxide oxygen, and the ring opens at the carbon better able to carry positive charge — the more substituted one.
Solvolysis of a crowded halide
A crowded carbon lets its leaving group go before anything arrives. The flat intermediate is then attacked from either face, so any configuration it had is lost.
Alkylation of an amine
An amine attacks an alkyl halide and takes its carbon, becoming a more substituted amine.
Alkylation of a thiol
A thiol or its anion attacks an alkyl halide and takes its carbon, leaving a thioether.
Mitsunobu coupling
A phosphine and an azodicarboxylate turn an alcohol into a leaving group where it stands, and an acidic partner displaces it.