Q: What is the observed rotation ($$\alpha_{\text{observed}}) if a $$solution of a chiral compound has a specific rotation $$[\alpha] = +50^\circ$$, a concentration $$c = 0.2 g/mL$$, and a sample cell length $$l = 2 dm$$?

$$\alpha_{\text{observed}} = +20^\circ$$

Question 1

Which of the following statements best describes a chiral molecule?

Accepted Answer

A molecule that is not superimposable on its mirror image.

Question 2

According to the Cahn-Ingold-Prelog convention, which group has the highest priority when assigning configuration to a chiral center?

Accepted Answer

$$\mathrm{Br}$$

Question 3

Which of the following is true about enantiomers?

Accepted Answer

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

Question 4

A molecule has two chiral centers. What is the maximum number of stereoisomers possible for this molecule?

Accepted Answer

$$4$$

Question 5

Which of the following best explains why only the S-isomer of ibuprofen is pharmacologically active?

Accepted Answer

The S-isomer fits the active site of the target enzyme due to its 3D configuration.

Question 6

Which of the following statements about Fischer projections is correct?

Accepted Answer

Vertical lines represent bonds going behind the plane of the paper.

Question 7

A compound has the following configuration at its only chiral center: the priorities are assigned as 1 (Br), 2 (OH), 3 (CH$$_3$$), 4 (H). When the lowest priority group (H) is in the back, the sequence 1-2-3 is counterclockwise. What is the configuration?

Accepted Answer

$$S$$

Question 8

Which of the following is a meso compound?

Accepted Answer

A compound with two chiral centers and an internal plane of symmetry.

Question 9

What is the observed rotation ($$\alpha_{	ext{observed}}) if a $$solution of a chiral compound has a specific rotation $$[\alpha] = +50^\circ$$, a concentration $$c = 0.2 g/mL$$, and a sample cell length $$l = 2 dm$$?

Accepted Answer

$$\alpha_{	ext{observed}} = +20^\circ$$

Question 10

Which of the following best describes the relationship between (R)-2-bromobutane and (S)-2-bromobutane?

Accepted Answer

They are enantiomers.

Question 11

A racemic mixture contains:

Accepted Answer

A 50:50 mixture of two enantiomers.

Question 12

Which of the following methods can be used to separate enantiomers in a racemic mixture?

Accepted Answer

Conversion to diastereomers followed by separation.

Question 13

Which of the following is NOT a property of enantiomers?

Accepted Answer

They have different chemical reactivity with achiral reagents.

Question 14

If a molecule has a plane of symmetry, it is:

Accepted Answer

Achiral.

Question 15

Which of the following best describes the difference between enantiomers and diastereomers?

Accepted Answer

Enantiomers are non-superimposable mirror images, while diastereomers are not mirror images.

Question 16

A sample of (R)-2-butanol has a specific rotation of $$+13.5^\circ. $$What would be the observed rotation for a racemic mixture of (R)- and (S)-2-butanol under identical conditions?

Accepted Answer

$$0^\circ$$

Question 17

Which of the following is a correct statement about the assignment of R and S configuration using the Cahn-Ingold-Prelog rules?

Accepted Answer

If the lowest priority group is in the back, assign R for clockwise and S for counterclockwise.

Question 18

Which of the following real-world examples demonstrates the importance of chirality in biology or medicine?

Accepted Answer

The different smells of R-carvone (spearmint) and S-carvone (caraway).

Question 19

Which of the following statements about the use of a polarimeter is correct?

Accepted Answer

A polarimeter is used to determine the optical rotation of a chiral compound.

Question 20

Which of the following is true about a 50:50 mixture of two enantiomers?

Accepted Answer

It is optically inactive because the rotations cancel each other.

Stereochemistry: Chirality, Stereoisomers, and Enantiomer Separation

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