Overall reaction
R–O⁻ Na⁺ + R′–X → R–O–R′ + NaX (R′ = methyl or primary)
An alkoxide or phenoxide displaces a halide from a methyl or primary alkyl halide (SN2).
Name reaction · mechanism
Williamson Ether Synthesis
The Williamson ether synthesis makes ethers by an SN2 reaction between an alkoxide (or phenoxide) and a methyl or primary alkyl halide. The example here deprotonates phenol with hydroxide and methylates the phenoxide with iodomethane to give anisole.
Mechanism step by step
- Phenoxide. Hydroxide removes the acidic O–H proton
- SN2. Phenoxide attacks the methyl carbon
Each step is checked electron by electron: the curly arrows give exactly the structures drawn.
Key points
- Use the hindered partner as the alkoxide and a methyl or 1° halide.
- Tertiary halides eliminate (E2) instead of substituting.
- Alcohols (pKa ≈ 16) need a stronger base such as NaH; phenols (pKa 10) need only NaOH.
- Intramolecular versions make cyclic ethers (epoxides, THF).
For JEE and NEET
- Put the bulky group on the alkoxide and use a methyl/primary halide.
- Tertiary halides give alkenes (E2) instead of ethers: tert-butyl methyl ether is made from (CH₃)₃CO⁻ + CH₃Br, not CH₃O⁻ + (CH₃)₃CBr.
- Aryl halides cannot be the electrophile: make aryl ethers from phenoxide + alkyl halide.
- Mechanism is SN2: inversion at the carbon attacked.
FAQ
Why can di-tert-butyl ether not be made by Williamson synthesis?
Any combination needs a tertiary halide, which undergoes E2 elimination with the strongly basic alkoxide.
Which combination gives anisole?
Sodium phenoxide + iodomethane (or dimethyl sulfate). Methoxide + bromobenzene does not react.
What is the mechanism of the Williamson synthesis?
A one-step SN2 backside attack of the alkoxide oxygen on the carbon bearing the halide.
Draw it in MolDraw
The button above opens the complete figure — overall reaction, numbered mechanism and key points — as ordinary editable structures. Change substituents, recolour atoms, or export a PNG, SVG or chemfig code for notes and slides. The same figure is in the Templates panel under Name reactions.