The aldehyde CH₃CH₂CH₂CHO reacts with KCN followed by dilute acid to form a racemic mixture of the two stereoisomers of CH₃CH₂CH(CH₃)(OH)CN - AQA - A-Level Chemistry - Question 4 - 2017 - Paper 2

To distinguish between the two stereoisomers, you can use polarized light. Enantiomers will rotate plane-polarized light in opposite directions, allowing you to identify the specific isomer based on the direction of rotation.

The reaction produces a racemic mixture because the nucleophile (CN⁻) can attack the carbonyl carbon of the aldehyde from either side with equal probability. This results in the formation of both enantiomers in equal amounts.

The structure of the compound formed is:

   CH₃
    | 
C - C - OH
    | 
   CH₂ - CN

This compound does not show stereoisomerism because it lacks a chiral center; all carbon atoms are attached to either hydrogen atoms or groups that do not create four different substituents.