Which of following ethers cannot be made by a Williamson ether synthesis?

Verified step by step guidance

1. Step 1: Understand the Williamson ether synthesis mechanism. It involves the reaction of an alkoxide ion (RO⁻) with a primary or secondary alkyl halide (R'X) via an SN2 mechanism to form an ether (ROR').
2. Step 2: Analyze the structures of the ethers provided (i, ii, iii, iv). Look for steric hindrance in the alkyl halide component, as SN2 reactions are hindered by bulky groups.
3. Step 3: For ether (i), the alkyl groups attached to the oxygen are relatively bulky, but the synthesis is possible if the alkyl halide is not overly hindered.
4. Step 4: For ether (ii), the alkyl groups are highly branched, and the formation of this ether via Williamson synthesis is unlikely due to steric hindrance preventing the SN2 reaction.
5. Step 5: For ethers (iii) and (iv), the alkyl groups are less hindered compared to ether (ii, making their synthesis via Williamson ether synthesis more feasible. Thus, ether (ii) cannot be made by Williamson ether synthesis.

Key Concepts

Williamson Ether Synthesis

Williamson ether synthesis is a method for creating ethers through the reaction of an alkoxide ion with a primary alkyl halide. This reaction involves nucleophilic substitution, where the alkoxide acts as a nucleophile, attacking the electrophilic carbon of the alkyl halide. The reaction is most effective with primary halides to avoid steric hindrance and elimination reactions.

Nucleophilicity and Sterics

Nucleophilicity refers to the ability of a nucleophile to donate an electron pair to form a bond with an electrophile. In the context of Williamson ether synthesis, steric hindrance plays a crucial role; bulky nucleophiles or electrophiles can hinder the reaction. Therefore, primary alkyl halides are preferred to minimize steric effects, while secondary or tertiary halides may lead to elimination rather than substitution.

Substitution Reactions

Substitution reactions involve the replacement of one functional group in a molecule with another. In Williamson ether synthesis, the reaction is typically an SN2 mechanism, where the nucleophile attacks the electrophile from the opposite side of the leaving group. Understanding the nature of the leaving group and the structure of the reactants is essential to predict the feasibility of the ether formation.