Q: A student prepares a chiral compound and measures its optical rotation as $$\alpha = 2.8^\circ$$ using $$0.0791 g/mL $$concentration and a $$1 dm $$path length. The literature value for $$[\alpha] is$$ $$42.3^\circ. $$What is the enantiomeric excess (%ee) of the sample?

$$\%ee = \dfrac{2.8}{0.0791 \times 1 \times 42.3} \times 100 = 84\%$$

Q: Which of the following is the correct formula for calculating enantiomeric excess (%ee)?

$$\%ee = \dfrac{\text{amount of desired enantiomer} - \text{amount of other enantiomer}}{\text{total amount}} \times 100$$

Question 1

Which of the following statements best describes a chiral molecule?

Accepted Answer

A molecule whose mirror image is not superimposable and has four different groups attached to a central carbon.

Question 2

A student prepares a chiral compound and measures its optical rotation as $$\alpha = 2.8^\circ$$ using $$0.0791 g/mL $$concentration and a $$1 dm $$path length. The literature value for $$[\alpha] is$$ $$42.3^\circ. $$What is the enantiomeric excess (%ee) of the sample?

Accepted Answer

$$\%ee = \dfrac{2.8}{0.0791 	imes 1 	imes 42.3} 	imes 100 = 84\%$$

Question 3

Which of the following is true about enantiomers?

Accepted Answer

They have identical boiling points, melting points, and solubility.

Question 4

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

Accepted Answer

$$2^2 = 4$

Question 5

Which of the following best describes a meso compound?

Accepted Answer

A compound with chiral centers and a plane of symmetry, making it achiral.

Question 6

Which statement about the interaction of chiral drugs with biological systems is correct?

Accepted Answer

Only one enantiomer typically interacts as intended, while the other may be inactive or cause side effects.

Question 7

Which of the following is the correct formula for calculating enantiomeric excess (%ee)?

Accepted Answer

$$\%ee = \dfrac{	ext{amount of desired enantiomer} - 	ext{amount of other enantiomer}}{	ext{total amount}} 	imes 100$$

Question 8

Which of the following is NOT a method chemists use to obtain a single enantiomer?

Accepted Answer

Heating a racemic mixture to high temperature.

Question 9

Which rule is used to assign priorities to groups attached to a chiral center?

Accepted Answer

Cahn-Ingold-Prelog rules, which assign priority based on atomic number.

Question 10

A molecule has the following groups attached to a chiral carbon: $$\mathrm{Cl}$$, $$\mathrm{CH_2OH}$$, $$\mathrm{C(CH_3$)_3}$$, and $$\mathrm{H}. $$What is the correct order of priority from highest to lowest?

Accepted Answer

$$\mathrm{Cl} \u003e \mathrm{CH_2OH} \u003e \mathrm{C(CH_3$)_3} \u003e \mathrm{H}$$

Question 11

Which of the following is true about geometric (E/Z) isomers?

Accepted Answer

They are a type of diastereomer that differ in the arrangement of groups around a double bond.

Question 12

How do you determine if an alkene is E or Z?

Accepted Answer

Assign priorities to the groups on each end of the double bond; if the higher priority groups are on the same side, it is Z; if on opposite sides, it is E.

Question 13

Which of the following is a correct statement about meso compounds?

Accepted Answer

They are achiral despite having chiral centers due to a plane of symmetry.

Question 14

Which of the following is true about the relationship between enantiomers and diastereomers?

Accepted Answer

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

Question 15

A compound with three chiral centers can have up to how many stereoisomers?

Accepted Answer

$$2^3 = 8$

Question 16

Which of the following is a consequence of the thalidomide tragedy in terms of stereochemistry?

Accepted Answer

One enantiomer was therapeutic, while the other caused severe birth defects.

Question 17

Which of the following is true about racemic mixtures?

Accepted Answer

They contain equal amounts of both enantiomers and are optically inactive.

Question 18

Which of the following is NOT a property shared by a pair of enantiomers?

Accepted Answer

Interaction with plane-polarized light.

Question 19

Which of the following is the correct way to assign R/S configuration to a chiral center?

Accepted Answer

Assign priorities to the four groups, orient the lowest priority group to the back, and trace from highest to lowest; clockwise is R, counterclockwise is S.

Stereoisomerism in Organic Chemistry: Enantiomers, Diastereomers, Meso Compounds, and Geometric Isomers

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