David H.

asked • 07/29/20

HELP FAST: When KCN then acid is added to buten-3-one, why does the alkene react faster than the carbonyl?

When buten-3-one is treated with 1.KCN and 2. H3O+, the product is CN-CH2CH2COCH3 (a chain with a ketone and nitrile).


Why does this occur? Isn't is more favorable for the KCN to react with the carbonyl carbon?

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Dylan S. answered • 07/29/20

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Hi David,


The resonance structure places a partial positive charge on the primary carbon, which makes it susceptible to a nucleophilic attack. Then keto-enol tautomerization occurs to regenerate the ketone. I can explicitly draw the mechanism if you need more clarification.


Best,


Dylan

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