Question

Predict the product(s) of treating the given alkyne with the reagents shown below. Show ALL atoms on chirality (stereo) centers, using wedge-and-dash bonds to indicate stereochemistry.

Answer 1

Concepts and reason

A reaction with two reagents is given and the product with the correct stereochemistry needs to be formed. Firstly, identify the reagent and the type of reaction that the substituents are undergoing. As the reagents are metal ion in liquid ammonia and then hydrogen gas over metal catalyst thus, the reactions are reduction reaction.

Now, according to the correct mechanism followed by both the reagents form the correct product.

Fundamentals

Generally metal ion in liquid ammonia is used for the reduction of alkynes to alkenes. The reaction is stereo selective in nature and result in the formation of trans alkenes as shown below:

Similarly, the reaction of hydrogen gas over metal surface is known as hydrogenation reaction and the hydrogen gets attached to the carbon from the same side of the double bond as shown below:

Firstly, draw the product of the reaction using reagent (1) as shown below:

Thus, alkyne is converted into trans alkene.

Now take the product of reaction 1 as the starting material for the reaction with the second reagent as shown below:

Thus, the alkene gets converted into alkane and the D is added from the same side.

Ans: