In a Williamson ether synthesis, which combination is needed to form an ether under SN2 conditions?

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Multiple Choice

In a Williamson ether synthesis, which combination is needed to form an ether under SN2 conditions?

In Williamson ether synthesis, forming an ether relies on SN2 displacement: a deprotonated alcohol (an alkoxide) acts as a nucleophile and attacks a carbon bearing a leaving group on an alkyl halide, displacing the halide and creating R–O–R. This works best when the nucleophile is a strong, unhindered alkoxide and the electrophile is a primary alkyl halide, which allows backside attack with minimal competing side reactions like elimination or carbocation rearrangements. The option with a good alkoxide and a primary alkyl halide fits this exactly: the alkoxide is the reactive nucleophile, and the primary halide provides a suitable, unhindered carbon for SN2 attack to yield the ether. The other pairings won’t form the ether under these conditions: a Grignard reagent would not combine with an alcohol to give an ether via SN2 and would be quenched by the alcohol; an aldehyde with an alcohol would form acetals/ hemiacetals under acid catalysis, not an ether via SN2; and a carboxylic acid with an alcohol would condense to an ester, not produce a Williamson ether.

In Williamson ether synthesis, forming an ether relies on SN2 displacement: a deprotonated alcohol (an alkoxide) acts as a nucleophile and attacks a carbon bearing a leaving group on an alkyl halide, displacing the halide and creating R–O–R. This works best when the nucleophile is a strong, unhindered alkoxide and the electrophile is a primary alkyl halide, which allows backside attack with minimal competing side reactions like elimination or carbocation rearrangements.

The option with a good alkoxide and a primary alkyl halide fits this exactly: the alkoxide is the reactive nucleophile, and the primary halide provides a suitable, unhindered carbon for SN2 attack to yield the ether. The other pairings won’t form the ether under these conditions: a Grignard reagent would not combine with an alcohol to give an ether via SN2 and would be quenched by the alcohol; an aldehyde with an alcohol would form acetals/ hemiacetals under acid catalysis, not an ether via SN2; and a carboxylic acid with an alcohol would condense to an ester, not produce a Williamson ether.

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