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Edexcel IAL Chemistry 15.5 Optical activity of reactants and products

Connect the stereochemical outcome to the mechanism: backside attack gives inversion, while planar carbonyls or carbocations allow attack from both sides.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • Link SN2 substitution to inversion and optical activity of a single product enantiomer.
  • Explain racemic carbonyl-addition products through attack on either face of planar C=O.
  • Infer mixed stereochemical outcomes when SN1 and SN2 pathways occur together.

15.5—Data on optical activity of reactants and products as evidence for SN1 and SN2 mechanisms and addition to carbonyl compounds question 1

[Maximum number: 2]

This question is about carbonyl compounds.

Another carbonyl compound, propanal, reacts with HCN in the presence of KCN to form a racemic mixture of two optical isomers of CH3CH2CH(OH)CN\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{OH}) \mathrm{CN}.

Explain, with reference to the reaction mechanism, why this reaction produces a racemic mixture.

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