Chapter 11, Problem 11.41P

Interpretation Introduction

Interpretation:

The acid-catalyzed hydration of the internal alkyne leads to only a single adduct (in low yield). [DK1] The product of the given reaction is to be drawn. The reason the mixture of adducts is not produced is to be explained.

Concept introduction:

Acid-catalyzed hydration of an alkyne produces a ketone. Step 1 is the electrophilic addition of ${\text{H}}^{\text{+}}$, which gives a resonance-stabilized vinylic carbocation intermediate. In step 2, water behaves as a nucleophile, attacking the positively charged C of that intermediate. ${\text{H}}^{\text{+}}$ is added preferentially to the terminal C in Step 1 to give the more stable carbocation intermediate. Water must then add to the internal C atom in the second step. Deprotonation in Step 3 produces the uncharged OH group, which is attached to an alkene C. The product is an enol. Under acidic conditions, the enol rapidly tautomerizes to the more stable keto form.