Below are two potential methods for preparing the same ether; but only one of them successful: Identify the successful approach: NaOMe Top method Bottom method Neither method, it is a trick question
The Correct Answer and Explanation is:
Williamson Ether Synthesis Overview:
- Reagents: Alkoxide (RO⁻) + Alkyl Halide (R’–X)
- Reaction: RO⁻ + R’–X → R–O–R’ + X⁻
- Condition: Works best when R’–X is primary, because secondary or tertiary halides tend to undergo E2 elimination instead.
Analyzing the Options (Hypothetical Representation)
Let’s assume the question gives two reaction pathways, such as:
Top Method:
Reacting NaOMe with methyl bromide (CH₃Br)
→ Reaction: CH₃O⁻ + CH₃Br → CH₃OCH₃ (dimethyl ether)
Bottom Method:
Reacting NaOMe with tert-butyl bromide (t-BuBr)
→ Reaction: CH₃O⁻ + (CH₃)₃C–Br → ?
Correct Answer: Top Method is Successful
Explanation
The successful method for synthesizing ethers using sodium methoxide (NaOMe) is the top method, which involves reacting NaOMe with methyl bromide. This reaction proceeds via an SN2 mechanism, where the methoxide ion (CH₃O⁻) acts as a nucleophile and directly displaces the bromide ion from the methyl group in a backside attack. Since methyl bromide is a primary alkyl halide, it is highly favorable for SN2 reactions. The result is a clean synthesis of dimethyl ether (CH₃OCH₃) with high yield and minimal side reactions.
In contrast, the bottom method, where NaOMe is reacted with tert-butyl bromide, fails to yield the ether product. This is because tert-butyl bromide is a tertiary alkyl halide, which is highly hindered and unsuitable for SN2 attack. Instead of substitution, the reaction favors E2 elimination, leading to the formation of isobutylene (2-methylpropene) rather than an ether. The bulky tert-butyl group prevents the methoxide from accessing the carbon center efficiently for nucleophilic substitution.
Therefore, the correct answer is: Top method.
The bottom method fails due to steric hindrance and competing elimination reactions.
This example underscores the importance of substrate selection in ether synthesis. Only primary alkyl halides should be used with strong nucleophiles like NaOMe in Williamson ether synthesis to avoid elimination and ensure high yields of the desired ether.
