Q74E - Organic Chemistry (Mcmurry)

Question

Reaction of 2-butanone with HCN yields a chiral product. What stereochemistry does the product have? Is it optically active?

Step-by-Step Solution

Answer

The product of the reaction of 2-butanone with HCN yields a mixture of two enantiomers so it is optically inactive.

Step 1: Racemic mixture

Racemic mixture is also called racemate, a mixture of equal quantities of two enantiomers or substance that have dissymmetric molecular structures that are mirror images of one another. Racemic mixtures are optically inactive in nature. For example thalidomide is the racemic mixture.

Step 2: Stereochemistry of the product

When any ketone reacts with hydrogen cyanide, we get hydroxyl nitrile. So, when 2-butanone reacts with HCN, it gives 2-Hydroxy-2-methylbutanenitrile.

(S)2-Hydroxy-2-methylbutanenitrile

(R)2-Hydroxy-2-methylbutanenitrile

                         Racemic mixture of the reaction of two enantiomers 

The carbonyl chromophore present on the 2-butanone is planar so HCN can add from both sides with equal ease. So the product of the reaction of 2-butanone with HCN yields a mixture of two enantiomers so it is optically inactive.