(a) Define the following: (i) Enantiomers (ii) Racemic mixture
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Enantiomers can be separated by chiral chromatography, and racemic mixtures can be resolved into their constituent enantiomers using techniques like recrystallization or enzymatic methods.
Enantiomers are stereoisomers that are non-superimposable mirror images. They share identical physical and chemical properties, except for their interaction with plane-polarized light (optical activity) and reactions with other chiral molecules. Enantiomers rotate plane-polarized light by equal magnitudes but in opposite directions, designated as dextrorotatory (+) and levorotatory (−).
Example:
D-lactic acid and L-lactic acid are enantiomers.
(ii) Racemic Mixture:
A racemic mixture, also known as a racemate, is a 1:1 combination of a chiral molecule's two enantiomers. Due to the cancellation of their optical activities, racemic mixtures are optically inactive, meaning they do not rotate plane-polarized light. These mixtures frequently result from chemical reactions where chiral products arise from achiral reactants without the involvement of a chiral catalyst or enzyme.
Example:
Racemic tartaric acid consists of equal amounts of D-tartaric acid and L-tartaric acid.
