Chapter 12, Problem 12.16P

Interpretation Introduction

Interpretation:

The product of the given reaction is to be predicted.

Concept introduction:

Terminal alkynes undergo alkoxymercuration-reduction reaction in the presence of ethanol-THF as a solvent to yield a vinyl ether as the final product. The reaction takes place in accordance to Markovnikov’s rule. The ethoxy group in ethanol is bonded to the carbon atom that can better stabilize a positive charge. In step $\text{1}$, the $\text{Hg}$ atom is electron-poor which is attacked by an electron-rich triple bond. The result is a three-membered mercurium ion intermediate. In step $\text{2}$, the solvent acts as a nucleophile to open the ring. In step $\text{3}$, the positively charged $\text{O}$ atom is deprotonated. Reduction then occurs when ${\text{NaBH}}_{\text{4}}$ is added, in which $\text{Hg}$ containing the substituent is replaced by $\text{H}$. In the case of the terminal alkyne, the ethoxy group attacks the more substituted carbon to acquire more positive charge from $\text{Hg}$.