Chapter 11, Problem 11.15P

Interpretation Introduction

Interpretation:

The complete, detailed mechanism for the given reaction is to be drawn, and the major product is to be drawn for the same reaction.

Concept introduction:

The triple bond in alkynes is sufficiently electron rich. The pi electrons in alkynes are easily accessible, and hence they readily undergo electrophilic addition reactions. Alkynes undergo acid catalyzed hydration reactions to yield a ketone. Step 1 is the electrophilic addition of proton, which produces a resonance-stabilized vinylic carbocation intermediate. In Step 2, water behaves as a nucleophile, attacking the positively charged carbon atom of that intermediate. Deprotonation in Step 3 produces the uncharged OH group, which is attached to an alkene carbon. The product of Step 3 is an enol. Under these conditions, the enol tautomerizes to the more stable keto form. Tetrafluoromethanesulfuric acid, also known as triflic acid, and 2, 2, 2-trifluoroethanol make it a strong acid that can be used as a catalyst in the acid-catalyzed hydration reactions of alkynes.