Williamson Ether Synthesis usually takes place as an S_N2 reaction of a primary or secondary alkyl halide with an alkoxide ion. Tertiary alkyl halides undergo elimination reactions readily rather than S_N2 under Williamson Ether Synthesis conditions. Tertiary alkyl halides produces alkene via elimination reaction.

Answer:

In Williamson's synthesis, tertiary alkyl halides cannot be used because they readily decompose to give olefin along with ethers. This is due to the stability of tertiary carbocations and the elimination reaction that occurs under the reaction conditions.

Explanation:

Williamson's synthesis: Williamson's synthesis is a method used to prepare ethers by the reaction of alkyl halides with alkoxides. The reaction involves the nucleophilic substitution of the halide by the alkoxide.

Tertiary alkyl halides: Tertiary alkyl halides are compounds in which the halogen atom is attached to a carbon atom that is bonded to three other carbon atoms. These compounds have a highly branched structure and are sterically hindered.

Decomposition to give olefin: Tertiary alkyl halides readily undergo elimination reactions, where the halide is eliminated along with the formation of a double bond (olefin). This is due to the stability of tertiary carbocations, which can be formed during the reaction.

Reactivity: Tertiary alkyl halides are less reactive compared to primary and secondary alkyl halides due to the steric hindrance caused by the three alkyl groups attached to the carbon atom. This steric hindrance makes it difficult for the nucleophile (alkoxide) to attack the carbon atom and undergo substitution.

Reversibility of the reaction: The reaction between tertiary alkyl halides and alkoxides is reversible. The formation of the olefin is favored under the reaction conditions, leading to an equilibrium between the reactants and products. This makes it difficult to obtain a high yield of the desired ether product.

Difficulty in removing the halogen atom: Tertiary alkyl halides are more stable compared to primary and secondary alkyl halides, making it difficult to remove the halogen atom. The C-X bond in tertiary alkyl halides is stronger and less reactive, requiring harsher reaction conditions to cleave the bond.

Overall, the combination of the decomposition of tertiary alkyl halides to give olefin along with ethers, their low reactivity, and the reversibility of the reaction make them unsuitable for use in Williamson's synthesis.