Question 1

Which of the following statements best explains why (S)-naproxen is preferred over (R)-naproxen in pharmaceutical formulations?

Accepted Answer

(R)-naproxen is a liver toxin, while (S)-naproxen is therapeutically active and safer.

Question 2

A molecule with two chiral centers can have a maximum of how many stereoisomers?

Accepted Answer

$$2^2 = 4$

Question 3

Which of the following is NOT a property that distinguishes diastereomers from enantiomers?

Accepted Answer

Enantiomers have different molecular formulas.

Question 4

A racemic mixture contains:

Accepted Answer

Equal amounts of two enantiomers and is optically inactive.

Question 5

Which of the following best describes a meso compound?

Accepted Answer

A compound with chiral centers that is achiral due to a plane of symmetry.

Question 6

The specific rotation $$[\alpha]_D of a $$sample is measured as $$+20^	ext{o}$$, while the pure enantiomer has $$[\alpha]_D = +40^	ext{o}. $$What is the optical purity of the sample?

Accepted Answer

$$50\%$$

Question 7

Which of the following is the correct method for assigning (R) or (S) configuration to a chiral center?

Accepted Answer

Assign priorities based on atomic number, orient the lowest priority group in the back, and trace from highest to lowest priority. Clockwise is (R), counterclockwise is (S).

Question 8

Which of the following best explains why thalidomide caused birth defects when administered as a racemic mixture?

Accepted Answer

One enantiomer is therapeutic, while the other is teratogenic (causes birth defects).

Question 9

Which of the following statements about enantiomers is TRUE?

Accepted Answer

They have identical physical properties except for the direction in which they rotate plane-polarized light.

Question 10

A solution contains 80% (R)-enantiomer and 20% (S)-enantiomer. What is the enantiomeric excess (ee)?

Accepted Answer

$$ee = 80\% - 20\% = 60\%$$

Question 11

Which of the following is a correct statement about Fischer projection formulas?

Accepted Answer

Horizontal lines represent bonds coming toward the viewer, and vertical lines represent bonds going away from the viewer.

Question 12

Which of the following is a method commonly used to resolve a racemic mixture of enantiomers?

Accepted Answer

Conversion to diastereomers followed by separation.

Question 13

Which of the following best describes a chiral center?

Accepted Answer

A tetrahedral atom, most commonly carbon, bonded to four different groups.

Question 14

Which of the following molecules is most likely to be achiral?

Accepted Answer

A molecule with a plane of symmetry.

Question 15

Which of the following is true regarding the interaction of chiral drugs with biological systems?

Accepted Answer

Enantiomers can interact differently with chiral biological molecules such as enzymes.

Question 16

Which of the following is the correct formula for calculating specific rotation?

Accepted Answer

$$[\alpha]_D = \frac{\alpha_{	ext{observed}}}{l \cdot c}$$

Question 17

Which of the following is a correct statement about the number of stereoisomers possible for a molecule with n chiral centers?

Accepted Answer

The maximum number is $$2^n.$$

Question 18

Which of the following best describes the difference between constitutional isomers and stereoisomers?

Accepted Answer

Constitutional isomers differ in connectivity, while stereoisomers have the same connectivity but differ in spatial arrangement.

Question 19

Which of the following is a correct statement about the physical properties of enantiomers?

Accepted Answer

They have identical physical properties except for the direction of rotation of plane-polarized light.

Question 20

Which of the following is a real-world consequence of chirality in pharmaceuticals, as illustrated by the thalidomide case?

Accepted Answer

One enantiomer can be therapeutic while the other can be harmful, leading to severe side effects.

Chirality and Stereochemistry: Pharmaceutical and Biological Applications

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