Objectives
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](http://chem.libretexts.org/@api/deki/files/84951/8-13.png?origin=mt-web)
Exercises
Question
1.
Predict the products of the following reaction showing stereochemistry.
![](https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/1518/2017/10/05143158/8-13qu.png)
Solution
1.
Contributors
- Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University)
- Prof. Steven Farmer (Sonoma State University)