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SN2 reaction of alkoxide ions with alkyl halides to give ethers (Williamson synthesis)

Description: Alkyl halides (or tosylates) will react with alkoxy ions to form ethers. This reaction is called the Williamson ether synthesis.

Notes: X here is a halide (Cl, Br, I) or sulfonate (OTs, OMs). The counter-ion on the alkoxy ion can be any alkali metal (e.g. Li, Na, K)

Examples: 

Notes: Note that since this is an SN2 reaction and proceeds via backside attack, there will be inversion of configuration at the carbon (note the last two examples). Note that in the second example that this ether would be difficult to make the opposite way (CH3O- attacking a tertiary alkyl bromide) since SN2 reactions don’t work on tertiary centers.

Mechanism: In the SN2 reaction the nucleophile (RO-) attacks the carbon with the good leaving group, forming a C–O bond and breaking the C–Br bond (Step 1, arrows A and B).

Notes: Again, the Na(+) is not crucial here, it’s just a spectator ion.