Question

The number of stereoisomers formed in a reaction of (±) Ph (C = O) C (OH) (CN) Ph with HCN is_____.
[Where, Ph is – C₆H₅]

Answer 1

Correct Answer: 3

To determine the number of stereoisomers formed in the reaction of (±) Ph(C=O)C(OH)(CN)Ph with HCN, we start by analyzing the stereochemistry involved. The initial molecule has a chiral center at C(OH)(CN), giving it two enantiomers in its racemic form (R and S configurations).
The reaction with HCN introduces a nucleophile (CN^-) to the carbonyl group (C=O), generating a new chiral center adjacent to the existing one due to the formation of a cyanohydrin.

Each chiral center can exist in either the R or S configuration, and their combinations result in different stereoisomers. The formula to determine the number of stereoisomers is 2ⁿ, where n is the number of chiral centers.

In this reaction:

• Initial chiral center: 1
• New chiral center from cyanohydrin formation: 1

Total chiral centers = 2.

Thus, the number of stereoisomers = 2² = 4.

This computation shows the number of stereoisomers formed (4) falls within the specified range of 3 to 3, verifying the reaction produces an expected diversity in stereochemistry.