$$EE = 100\% \times \frac{[\alpha]_{mixture}}{[\alpha]_{pure}}$$

Question 1

Which of the following statements best describes a stereoisomer?

Accepted Answer

A compound with the same connectivity but a different arrangement of atoms in space.

Question 2

What is the minimum requirement for a carbon atom to be considered asymmetric?

Accepted Answer

It must be bonded to four different groups.

Question 3

Which of the following molecules is chiral?

Accepted Answer

2-butanol

Question 4

A molecule with a plane of symmetry is always:

Accepted Answer

Achiral

Question 5

Which of the following is true about enantiomers?

Accepted Answer

They have identical physical properties except for their interaction with plane-polarized light.

Question 6

How do you distinguish between two enantiomers in the laboratory?

Accepted Answer

By their interaction with plane-polarized light.

Question 7

What is the formula for calculating enantiomeric excess (EE) from optical rotation?

Accepted Answer

$$EE = 100\% 	imes \frac{[\alpha]_{mixture}}{[\alpha]_{pure}}$$

Question 8

A sample contains 80% (+)-enantiomer and 20% (–)-enantiomer. What is the net optical activity compared to the pure (+)-enantiomer?

Accepted Answer

60%

Question 9

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

Accepted Answer

It has identical physical properties to pure enantiomers.

Question 10

Which statement about diastereomers is correct?

Accepted Answer

Diastereomers differ in all their physical properties.

Question 11

How many stereoisomers are possible for a molecule with two stereocenters, assuming no meso compound is present?

Accepted Answer

$$2^2 = 4$

Question 12

Which of the following is a characteristic of meso compounds?

Accepted Answer

They have an internal mirror plane.

Question 13

Which of the following best describes the process of racemization?

Accepted Answer

The formation of a racemate from a pure enantiomer.

Question 14

Which method is commonly used for the resolution of enantiomers?

Accepted Answer

Chiral chromatography.

Question 15

What is the relationship between the R/S configuration and the sign of optical rotation?

Accepted Answer

There is no direct relationship between R/S configuration and the sign of optical rotation.

Question 16

Which of the following molecules can exhibit chirality without an asymmetric center?

Accepted Answer

2,3-pentadiene (an allene)

Question 17

What is the effect of amine inversion on the separation of enantiomers of ethylmethylamine?

Accepted Answer

It prevents separation because the enantiomers rapidly interconvert.

Question 18

Which of the following is true about the physical properties of enantiomers and diastereomers?

Accepted Answer

Enantiomers have identical physical properties except for optical activity, while diastereomers differ in all physical properties.

Question 19

A mixture contains 70% of the major enantiomer and 30% of the minor enantiomer. What is the enantiomeric excess (EE)?

Accepted Answer

$$EE = 70\% - 30\% = 40\%$$

Question 20

Which of the following is a correct statement about the number of stereoisomers for 2,3-butanediol?

Accepted Answer

There are three stereoisomers due to the presence of a meso compound.

Principles of Stereochemistry (Chapter 6): Enantiomers, Chirality, and Diastereomers

Study Guide - Practice Questions