Q: A solution of (S)-2-iodobutane has a specific rotation of $$+15.90^\circ. If a $$mixture of (R)- and (S)-2-iodobutane has a specific rotation of $$-3.18^\circ$$, what is the enantiomeric excess (ee) of the mixture?

$$ee = \frac{3.18}{15.90} \times 100 = 20\%$$

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

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

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

Which of the following compounds is achiral?

Accepted Answer

A molecule with a plane of symmetry.

Question 3

What is the maximum number of stereoisomers possible for a molecule with three chiral centers, assuming no plane of symmetry?

Accepted Answer

$$2^3 = 8$

Question 4

Which of the following is true about enantiomers?

Accepted Answer

They have identical physical properties except for their interaction with plane-polarized light and other chiral molecules.

Question 5

A solution of (S)-2-iodobutane has a specific rotation of $$+15.90^\circ. If a $$mixture of (R)- and (S)-2-iodobutane has a specific rotation of $$-3.18^\circ$$, what is the enantiomeric excess (ee) of the mixture?

Accepted Answer

$$ee = \frac{3.18}{15.90} 	imes 100 = 20\%$$

Question 6

Which of the following best describes a meso compound?

Accepted Answer

A compound with a plane of symmetry and is achiral despite having chiral centers.

Question 7

Which of the following is NOT a property of a racemic mixture?

Accepted Answer

It rotates plane-polarized light.

Question 8

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

Accepted Answer

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

Question 9

Which of the following statements about the Cahn–Ingold–Prelog priority rules is correct?

Accepted Answer

Double bonds are treated as if each atom is bonded to two separate atoms.

Question 10

A compound has two chiral centers and a plane of symmetry. How many stereoisomers does it have?

Accepted Answer

3

Question 11

Which of the following best describes diastereomers?

Accepted Answer

Stereoisomers that are not mirror images of each other.

Question 12

Which of the following is a correct statement about the separation of enantiomers?

Accepted Answer

Enantiomers can be separated by reacting them with a pure chiral compound to form diastereomers.

Question 13

Which of the following is true about the optical activity of enantiomers?

Accepted Answer

Both enantiomers rotate plane-polarized light by the same magnitude but in opposite directions.

Question 14

Which of the following is NOT allowed when manipulating Fischer projections?

Accepted Answer

Rotating the projection by 90° in the plane.

Question 15

Which of the following statements about meso compounds is correct?

Accepted Answer

Meso compounds have chiral centers but are achiral due to an internal plane of symmetry.

Question 16

Which of the following best describes the relationship between cis- and trans-1,2-dichlorocyclohexane?

Accepted Answer

They are diastereomers.

Question 17

Which of the following is a correct statement about the effect of a racemic mixture on plane-polarized light?

Accepted Answer

It does not rotate plane-polarized light.

Question 18

Which of the following is a correct application of the Cahn–Ingold–Prelog rules for assigning (R) and (S) configuration?

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 19

Which of the following is a real-world example of the importance of stereochemistry?

Accepted Answer

Enantiomers of a drug can have different biological activities, such as one being therapeutic and the other being inactive or harmful.

lecture 5 Stereochemistry: Chirality, Stereoisomers, and Optical Activity

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