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8.13: Stereochemistry of Reactions - Addition of H₂O to a Chiral Alkene

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    Objective

    After completing this section, you should be able to explain why the addition of H2O to a chiral alkene leads to unequal amounts of diastereomeric products.

    Study Notes

    In the previous section, the addition of water to the achiral alkene produced a racemic mixture of two enantiomeric alcohols. They are produced in equal amounts so the mixture is optically inactive. What would occur if we carried out a similar reaction on a chiral alkene? Consider (S)-3-methyl-1-pentene reacting with water (acid catalyzed). Proton addition produces a carbocation intermediate that is chiral (* denotes stereogenic centre). That intermediate does not have a plane of symmetry and therefore attack by water is not equal from the top and bottom. This ultimately produces R and S products in a non 50:50 ratio. 

    alkene hydration giving a non-racemic mixture of stereoisomers

    Exercise

    Exercise \(\PageIndex{1}\)

    Predict the products of the following reaction showing stereochemistry.

    8.13qu.png

    Answer

     8.13sol.png

    The products are diastereomers of one another.

    Contributors and Attributions

    8.13: Stereochemistry of Reactions - Addition of H₂O to a Chiral Alkene is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.