Illustrate with example the limitations of Williamson synthesis for the preparation of certain type of ethers .

Explanation

Following type of enthers cannot be prepared by Williamson synthesis
(i) Symmetrical or unsymmetrical ethers containing secondary or tertiary alkyl groups cannot be prepared by Williamson synthesis . For example ,
`CH_(3)-overset(CH_(3))overset(|)(CH)-Br+CH_(3)-overset(CH_(3))overset(|)(CH)-ONaunderset(-NaBr)overset(Delta)to`
`underset("Propene")(CH_(3)-CH=CH_(2))+underset("Isopropyl alcohol")(CH_(3)-overset(CH_(3))overset(|)(CH)-OH)+underset("Minor product")underset("Di -isopropyl ether")(CH_(3)-overset(CH_(3))overset(|)(CH)-O-overset(CH_(3))overset(|)(CH)-)CH_(3)`
This is due to the fact that `2^(@)and3^(@)` alkyl halides , due to steric hinderance , prefer to undergo elimination rather than substitution .
(ii) Symmetrical or unsymmetrical diary ethers cannot be prepared by Williamson synthesis . For example ,sodium phenoxide does not react with bramobenzene to give diphenyl ether This is because aryl halides do not undergo nucleophilic substitution easily .