Reaction of alkyl halides with water to form alcohols (SN1)

by James

Description: Alkyl halides will react with water to form alcohols through an SN1 mechanism.
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Notes: X is a halide such as Cl, Br, or I (never F). The R group must be able to form a stable carbocation (e.g. tertiary, benzylic or allylic).

In these reactions water is generally used as the solvent.

Examples: 

Notes: Note that if the alkyl halide is on a stereocenter, a 1:1 mixture of stereoisomers will be obtained (example 3).

Mechanism: Cleavage of the C–Cl bond (Step 1, arow A) leads to the carbocation, which is attacked by water (Step 2, arrows B). Deprotonation of the oxygen (Step 3, arrows C and D) leads to the alcohol. This is an SN1 reaction.

Notes: It’s probably more reasonable to show water as the base in step C. Note that if C-2 was a stereocenter, this reaction would end up as a mixture of stereoisomers.

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{ 3 comments… read them below or add one }

Omar Sadek

Looking forward to becoming a member. This is a great site. I wish I would have found it earlier.

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Michel Carroll

I’ve heard it mentioned that dilute acid can be used to transform RX into ROH. In that case, would the reaction follow this same pathway (Sn1), or would it be a different mechanism?

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Mark Quercioli

Great example!! I think you were suppose to say cleavage of C-Cl in step 1 instead of C-Br though. Regardless, X is a halide. Thank you for this awesome website. I love being a member!!

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