Chapter 17: Aldehydes and Ketones. Nucleophilic Additionto C=O |
Summary
MECHANISM FOR
REACTION OF ALKYNES WITH H3O+ |
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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. |
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Step 2: Attack of the nucleophilic water molecule on the electrophilic carbocation creates an oxonium ion. |
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Step 3: An acid / base reaction. Deprotonation by a base generates the alcohol and regenerates the acid catalyst forming an unstable enol. |
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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. |
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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. |
© Dr. Ian Hunt, Department of Chemistry |