If a tertiary alkyl halide is used, an alkene is the only reaction product and no ether is formed. For example, the reaction of CH3​ONa with (CH3​)3​C−Br gives exclusively 2-methylpropene. CH3​−CH3​∣C∣CH3​​​−Br + Na+O− - CH3​ → 2-MethylpropeneCH3​−CH3​∣C​​=CH2​​ + NaBr + CH3​OH It is because alkoxides are not only nucleophiles but strong bases as well. They react with alkyl halides leading to elimination reactions.