Hi,

Williamson synthesis takes place via S_N2 mechanism. 

An example is the reaction of sodium ethoxide with chloroethane to form diethyl ether and sodium chloride:

Na⁺C₂H₅O⁻ + C₂H₅Cl → C₂H₅OC₂H₅ + Na⁺Cl⁻

Thanks for asking 

Good day :)