Illustrate with examples the limitations of the Williamson's synthesis for the preparation of certain types of ethers.

Explanation

Williamson.s synthesis is not applicable for tertiary alkyl halides as they yield alkenes instead of ethers.
The reaction of `CH_(3)ONa` with `(CH_(3))_(3)C-Br` gives exclusively, 2-methyl propene.
`underset("teret-butyl bromide")(CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)(C)-Br)+Na-underset(••)overset(••)(O)-CH_(3)tounderset("2-methyl propene")(CH_(3)-underset(CH_(3))underset(|)(C)=CH_(2)+)NaBr`
(ii) Aryl and vinyl halides cannot be used as substrates because of their low reactivity in nucleophilic substitution.