Organic 2 Section 3 - Unit 25: Nomenclature and Isomerism
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State the meaning of the term racemic mixture and explain how racemic mixtures occur (3 marks)
• Optically inactive/equal mixture of enantiomers • Occur when a planar carbonyl group • Attack from above or below (either side)
Explain how you could distinguish between optical isomers (2 marks)
• Plane polarised light - Rotated in opposite/different directions
Butanone is reduced in a two-step reaction using NaBH4 followed by dilute hydrochloric acid. By considering the mechanism of the reaction, explain why the product has no effect on plane polarised light (6 marks)
Stage 1: Formation of product - Nucleophilic attack - Planar carbonyl group - H – attacks from either side Stage 2: Nature of product • Product exists in two chiral forms • Equal amounts of each enantiomer/racemic mixture formed Stage 3: Optical activity - Optical isomers/enantiomers rotate the plane of polarised light equally in - With a racemic mixture the effects cancel