Question

(a) Define the following:
(i) Enantiomers 
(ii) Racemic mixture

Hint:

Enantiomers can be separated by chiral chromatography, and racemic mixtures can be resolved into their constituent enantiomers using techniques like recrystallization or enzymatic methods.

Answer 1

(i) Enantiomers:

Enantiomers are a pair of stereoisomers that are non-superimposable mirror images of each other. They have 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 in equal magnitudes but opposite directions (one being dextrorotatory [+] and the other levorotatory [−]).

Example: The two forms of lactic acid (D-lactic acid and L-lactic acid) are enantiomers.

(ii) Racemic Mixture:

A racemic mixture (or racemate) is a 1:1 mixture of two enantiomers of a chiral molecule. Because the optical activities of the enantiomers cancel each other out, a racemic mixture is optically inactive (does not rotate plane-polarized light). Racemic mixtures are often formed in chemical reactions where a chiral product is generated from achiral reactants without the use of a chiral catalyst or enzyme.

Example: Racemic tartaric acid is an equal mixture of D-tartaric acid and L-tartaric acid.