For a primary alkyl chloride in water, which mechanism dominates and what is the likely product?

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Multiple Choice

For a primary alkyl chloride in water, which mechanism dominates and what is the likely product?

The key idea is that a primary carbon with a chlorine leaving group is best attacked by a nucleophile in a single, concerted step. In water, the nucleophile is the water molecule. Because the carbon bearing the leaving group is only lightly substituted, backside attack by water can occur readily, displacing chloride in one step. This is SN2, a bimolecular substitution where the rate depends on both the substrate and the nucleophile. Why SN1 isn’t favored here helps understand the choice: SN1 would involve forming a primary carbocation, which is very unstable, so that pathway is not competitive for a primary alkyl chloride in water. E2 requires a strong base to pull off a proton and form an alkene, which isn’t the situation in neutral water; water is a weak base, so elimination is unlikely. After water attacks, you get an oxonium intermediate that is deprotonated to give the alcohol. If the carbon were chiral, SN2 would invert the configuration at that center. So the dominant route is SN2, yielding a primary alcohol as the product.

The key idea is that a primary carbon with a chlorine leaving group is best attacked by a nucleophile in a single, concerted step. In water, the nucleophile is the water molecule. Because the carbon bearing the leaving group is only lightly substituted, backside attack by water can occur readily, displacing chloride in one step. This is SN2, a bimolecular substitution where the rate depends on both the substrate and the nucleophile.

Why SN1 isn’t favored here helps understand the choice: SN1 would involve forming a primary carbocation, which is very unstable, so that pathway is not competitive for a primary alkyl chloride in water. E2 requires a strong base to pull off a proton and form an alkene, which isn’t the situation in neutral water; water is a weak base, so elimination is unlikely.

After water attacks, you get an oxonium intermediate that is deprotonated to give the alcohol. If the carbon were chiral, SN2 would invert the configuration at that center.

So the dominant route is SN2, yielding a primary alcohol as the product.

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