Question

Which of the following ethers cannot be prepared by the Williamson ether synthesis? A) Isopropyl methyl ether B) tert-Butyl methyl ether C) tert-Butyl phenyl ether D) Methyl phenyl ether

Answer 1

OPTION B.

Tert-Butyl methyl ether cannot be prepared by the Williamson ether synthesis due to steric hindrance that leads to elimination reactions rather than substitution when using tertiary alkyl halides.

Step-by-step explanation:

The ether that cannot be prepared by the Williamson ether synthesis is tert-Butyl methyl ether (B). Williamson ether synthesis typically involves the reaction of an alkoxide ion with a primary alkyl halide. Due to steric hindrance, tertiary alkyl halides, like tert-butyl halide, cannot be used because they tend to undergo elimination reactions rather than the desired substitution to form the ether. Therefore, it is problematic to use this method to synthesize ethers that would require a tertiary alkyl halide as a reactant, such as tert-Butyl methyl ether.

Answer 2

Answer: C) tert-Butyl phenyl ether

Step-by-step explanation:

n Williamson ether synthesis, an alcohol is treated with an alkyl halide in presence of a strong base such as sodium hydride (NaH), to form an ether. Initially, an alkoxide ion is formed by the reaction of the alcohol with sodium hydride (NaH). The alkoxide ion then acts as a nucleophile and attacks alkyl halide to form an ether. The reaction is represented as follows:

\text{ROH}\xrightarrow{\text{NaX}}\text{R}{{\text{O}}^{-}}\text{ N}{{\text{a}}^{+}}\xrightarrow{\text{R }\!\!'\!\!\text{ }-\text{X}}\text{R}-\text{O}-\text{R }\!\!'\!\!\text{ }

The R’-X used in the given reaction is generally a primary alkyl halide, which suggests that one of the hydrocarbon chains in the product ether will be a primary alkyl group. In the given ether, the two alkyl groups are the isopropyl group and the methyl group. The methyl group is a primary alkyl group, which suggests that the given ether can be prepared by Williamson ether synthesis. As a result, option A is incorrect.

In the given ether, the two alkyl groups are the tert-Butyl group and the methyl group. The methyl group is a primary alkyl group, which suggests that the given ether can be prepared by Williamson ether synthesis. As a result, option B is incorrect.

In the given ether, one is tert-Butyl group and the other is phenyl group. None of the two hydrocarbon groups is a primary alkyl group, which suggests that the given ether can not be prepared by Williamson ether synthesis. As a result, option C is the correct choice.

In the given ether, one is methyl group and the other is phenyl group. The methyl group is a primary alkyl group, which suggests that the given ether can be prepared by Williamson ether synthesis. As a result, option D is incorrect.