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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
Question 4
The aldehyde CH₃CH₂CH₂CHO reacts with KCN followed by dilute acid to form a racemic mixture of the two stereoisomers of CH₃CH₂CH(CH₃)(OH)CN. 1. Give the IUPAC name ... show full transcript
Worked Solution & Example Answer: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
Step 1
Step 2
Describe how you would distinguish between separate samples of the two stereoisomers of CH₃CH₂CH(CH₃)(OH)CN.
Answer
You can distinguish between the two stereoisomers by using plane-polarized light. Enantiomers will rotate the light in opposite directions. Thus, by passing the light through a sample of each stereoisomer, you will observe different angles of rotation.
Step 3
Explain why the reaction produces a racemic mixture.
Answer
The reaction produces a racemic mixture because the addition of KCN to the carbonyl compound occurs at the planar carbonyl group from either side with equal probability. This leads to the formation of both enantiomers in equal amounts.
Step 4
An isomer of CH₃CH₂CH₂CHO reacts with KCN followed by dilute acid to form a compound that does not show stereoisomerism.
Answer
The compound formed is 2-hydroxy-2-methylpropanenitrile, which can be represented as follows:
Structure:
OH
|
CH₃-C-CH₃
|
CN
Justification: This compound does not exhibit stereoisomerism because it does not contain a chiral center; the carbon attached to the OH group is also bonded to two identical groups (the two CH₃ groups), thus leading to symmetry.