Alkene hydration
Water adds across a double bond. The hydrogen goes to the carbon that already has more of them and the hydroxyl to the other, so the more substituted alcohol is the one that forms.
What it needs, and what it gives
- Reaction class
- Addition
- Water with an acid catalyst. A borane instead gives the other alcohol, by hydroboration.
- balanced — the co-products are written out, not dropped
- Mechanism
- Acid-catalysed hydration of an alkene, 3 steps
How it is thought to happen
Acid gives the alkene a proton, leaving a positively charged carbon; water attacks it and then loses a proton, and the acid is returned.
- The alkene takes a proton from the acid
- Water attacks the charged carbon
- The acid is given back
Try it on your own structures
Enter your reactants in the Reaction Lab. If this transformation matches what you drew, it is applied and the outcome is shown next to the records that back it — with the count of documented reactions doing the same thing on substrates like yours, rather than a confidence score.
Other addition transformations
Conjugate addition
A stabilised carbanion adds to the far end of an enone rather than to its carbonyl.
Organometallic addition to a carbonyl
The carbon of the organometallic adds to the carbonyl carbon; the alcohol appears on work-up.
Hydroboration of an alkene
Boron and hydrogen add across the double bond, boron to the less hindered carbon, and the carbon–boron bond is then replaced by a hydroxyl with retention. The alcohol ends up on the opposite carbon from the one acid-catalysed hydration would give.
Bromination of an alkene
Bromine adds across the double bond. The second bromide arrives on the opposite face from the first, so the two end up anti.
Dihydroxylation of an alkene
Two hydroxyls are delivered to the same face of the double bond, giving the cis diol.