Bcoz teritary alkyl halide prefer elimination rather then substitution.

Introduction:
Williamson's synthesis is a widely used method for the preparation of ethers. It involves the reaction of an alkoxide ion with an alkyl halide or an aryl halide. This reaction is an example of a nucleophilic substitution reaction.

Explanation:
To determine which compound cannot be made using Williamson's synthesis, we need to analyze the structure and functional groups of each compound.

a) Methoxybenzene:
Methoxybenzene, also known as anisole, has a methoxy group (-OCH3) attached to a benzene ring. This compound can be synthesized using Williamson's synthesis by reacting sodium methoxide (the alkoxide ion) with an alkyl halide or an aryl halide.

b) Benzyl p-nitrophenyl ether:
Benzyl p-nitrophenyl ether has a benzyl group (-CH2Ph) and a p-nitrophenyl group (-C6H4NO2) connected through an ether linkage. This compound can also be synthesized using Williamson's synthesis by reacting sodium benzylate (the alkoxide ion) with an alkyl halide or an aryl halide.

c) Methyl tertiary butyl ether:
Methyl tertiary butyl ether (MTBE) has a methyl group (-CH3) and a tertiary butyl group (-C(CH3)3) connected through an ether linkage. This compound can be synthesized using Williamson's synthesis by reacting sodium tert-butoxide (the alkoxide ion) with an alkyl halide or an aryl halide.

d) Di-tert. butyl ether:
Di-tert. butyl ether has two tert-butyl groups connected through an ether linkage. The tert-butyl group (-C(CH3)3) has three methyl groups attached to a tertiary carbon atom. This compound cannot be synthesized using Williamson's synthesis because the tert-butyl halide required for the reaction is not stable and tends to undergo elimination reactions rather than nucleophilic substitution reactions.

Conclusion:
Based on the analysis, the compound that cannot be made using Williamson's synthesis is di-tert. butyl ether. The other compounds (methoxybenzene, benzyl p-nitrophenyl ether, and methyl tertiary butyl ether) can be synthesized using this method.