Organic Chemistry MCAT Practice Exam

Which method would be used to separate enantiomers from a racemic mixture?

1. Add a polar solvent

2. Use a chiral resolving agent

3. Perform distillation without alteration

4. Increase temperature during extraction

The correct answer is: Use a chiral resolving agent

To separate enantiomers from a racemic mixture, the method involving a chiral resolving agent is effective because it takes advantage of the differences in the interactions of chiral molecules with a chiral environment. A resolving agent is typically a chiral compound that can form diastereomers with the enantiomers of the racemic mixture. Since diastereomers have different physical properties, such as solubility or boiling points, this allows for their separation through conventional separation techniques like crystallization or chromatography. Using a chiral resolving agent selectively interacts with one enantiomer more than the other, leading to distinct behavior in a separation process. For instance, if a chiral acid is used, it can react with one enantiomer to form a salt, which can then be isolated and purified with ease, leaving the unreacted enantiomer in the solution. The other methods mentioned would not effectively separate enantiomers because they either do not alter the relationship between the molecules significantly or rely on physical properties that do not differ enough in the case of enantiomers to facilitate separation. For example, adding a polar solvent might affect solubility but will not resolve the enantiomers' different spatial arrangements, and distillation without alteration assumes