Q: A chemist prepares $$(S)-$$propranolol with a specific rotation of $$-18.3^{\circ}$$, but the pure enantiomer has $$-25.5^{\circ}. $$What is the enantiomeric excess (ee) of the sample?

$$ee = \frac{18.3}{25.5} \times 100\% = 71.8\%$$

Question 1

Which of the following statements best describes a chiral molecule?

Accepted Answer

A molecule that is nonsuperimposable on its mirror image.

Question 2

Which of the following is true about enantiomers?

Accepted Answer

They rotate plane-polarized light in equal but opposite directions.

Question 3

A carbon atom with four different groups attached is called:

Accepted Answer

A stereocenter

Question 4

Which of the following best describes a racemic mixture?

Accepted Answer

A mixture containing equal amounts of two enantiomers.

Question 5

Which of the following molecules is achiral?

Accepted Answer

A molecule with a plane of symmetry.

Question 6

Using the Cahn–Ingold–Prelog (CIP) system, what is the absolute configuration if the path from priority 1 → 2 → 3 is clockwise with group 4 pointing away?

Accepted Answer

$$R$$

Question 7

Which of the following is NOT a property of diastereomers?

Accepted Answer

They have identical physical properties in all environments.

Question 8

A solution of $$(S)-2-$$bromobutane has a specific rotation of $$-23.1^{\circ}. $$What is the specific rotation of $$(R)-2-$$bromobutane?

Accepted Answer

$$+23.1^{\circ}$$

Question 9

How many stereoisomers are possible for a molecule with three stereocenters?

Accepted Answer

$$8$$

Question 10

Which of the following best describes a meso compound?

Accepted Answer

A compound with stereocenters and a plane of symmetry.

Question 11

A chemist prepares $$(S)-$$propranolol with a specific rotation of $$-18.3^{\circ}$$, but the pure enantiomer has $$-25.5^{\circ}. $$What is the enantiomeric excess (ee) of the sample?

Accepted Answer

$$ee = \frac{18.3}{25.5} 	imes 100\% = 71.8\%$$

Question 12

Which of the following statements about the relationship between $$(R)/(S)$$ and $$(+)/(−) is $$correct?

Accepted Answer

There is no general relationship between $$(R)/(S)$$ and $$(+)/(−).$$

Question 13

Which of the following methods is commonly used to separate enantiomers in the laboratory?

Accepted Answer

Chromatography using a chiral stationary phase

Question 14

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

Accepted Answer

One enantiomer was an effective sedative, while the other was teratogenic.

Question 15

Which of the following is a correct application of the Cahn–Ingold–Prelog priority rules?

Accepted Answer

Assign highest priority to the group with the highest atomic number.

Question 16

A molecule with two stereocenters has only three stereoisomers. What is the most likely explanation?

Accepted Answer

One of the stereoisomers is a meso compound.

Question 17

Which of the following statements about Fischer projections is correct?

Accepted Answer

Horizontal bonds are coming out of the plane toward the viewer.

Question 18

Which of the following best describes atropisomerism?

Accepted Answer

Isomerism due to slow rotation around a bond, allowing isolation of enantiomers.

Question 19

Which of the following is a property of a racemic mixture?

Accepted Answer

It does not rotate plane-polarized light.

Stereoisomerism: Arrangement of Atoms in Space (Organic Chemistry Chapter 6)

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