Return to Contents  Chapter 17: Aldehydes and Ketones. Nucleophilic Additionto C=O  Ch 17 contents
Hydration of Alkynes
(review of Chapter 9)
hydration of alkynes
Reaction type: Electrophilic Addition


Step 1:
An acid / base reaction. Protonation of the alkyne to generate the more stable carbocation.  The π electrons act pairs as a Lewis base.
addition of H2O to alkynes
Step 2:
Attack of the nucleophilic water molecule on the electrophilic carbocation creates an oxonium ion.
Step 3:
An acid / base reaction. Deprotonation by a base generates the alcohol and regenerates the acid catalyst forming an unstable enol.
Step 4:
An acid / base reaction. Reprotonation by the acid catalyst occurson the carbon. The oxygen atom electrons help facilitate this process generating an oxonium ion.
Step 5:
Another acid / base reaction. Deprotonation of the oxonium ion createsthe ketone. Steps 4 and 5 show the acid catalysed tautomerisation of the enol to the ketone.

previous page
next page
organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary