|Chapter 17: Aldehydes and Ketones. Nucleophilic Additionto C=O|
MECHANISM FOR REACTION OF ALKYNES WITH H3O+
An acid / base reaction. Protonation of the alkyne to generate the more stable carbocation. The π electrons act pairs as a Lewis base.
Attack of the nucleophilic water molecule on the electrophilic carbocation creates an oxonium ion.
An acid / base reaction. Deprotonation by a base generates the alcohol and regenerates the acid catalyst forming an unstable enol.
An acid / base reaction. Reprotonation by the acid catalyst occurson the carbon. The oxygen atom electrons help facilitate this process generating an oxonium ion.
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.
|© Dr. Ian Hunt, Department of Chemistry, University of Calgary|