Q: A scientist observes that a pure sample of a chiral compound rotates plane-polarized light $$+15^ ext{o} in a 2 dm $$tube at a concentration of $$0.5\ \mathrm{g\ mL$$^{-1}$$}. $$What is the specific rotation $$[\alpha] of $$the compound?

$$+15^ ext{o}/(2 \times 0.5) = +15^ ext{o}/1 = +15^ ext{o}$$

Question 1

Which of the following statements best describes the difference between structural (constitutional) isomers and stereoisomers?

Accepted Answer

Structural isomers have the same molecular formula but different connectivity; stereoisomers have the same connectivity but differ in spatial arrangement.

Question 2

A solution contains 1 M $$(R)-2-$$butanol and 1 M $$(S)-2-$$butanol. What is the expected optical activity of this solution?

Accepted Answer

It will show no optical activity.

Question 3

Which of the following best explains why meso compounds are optically inactive?

Accepted Answer

They possess an internal plane of symmetry that cancels optical activity.

Question 4

How many possible stereoisomers exist for a molecule with three chiral centers?

Accepted Answer

$$8$$

Question 5

Which of the following is true about enantiomers?

Accepted Answer

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

Question 6

A scientist observes that a pure sample of a chiral compound rotates plane-polarized light $$+15^	ext{o} in a 2 dm $$tube at a concentration of $$0.5\ \mathrm{g\ mL$$^{-1}$$}. $$What is the specific rotation $$[\alpha] of $$the compound?

Accepted Answer

$$+15^	ext{o}/(2 	imes 0.5) = +15^	ext{o}/1 = +15^	ext{o}$$

Question 7

Which of the following conformations of butane is the most energetically favorable?

Accepted Answer

Anti staggered conformation

Question 8

Which of the following best describes the relationship between $$(R)-2-$$chloro-$$(S)-3-$$bromobutane and $$(S)-2-$$chloro-$$(R)-3-$$bromobutane?

Accepted Answer

They are diastereomers.

Question 9

Which of the following statements about racemic mixtures is correct?

Accepted Answer

They contain equal amounts of both enantiomers and show no net optical activity.

Question 10

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

Accepted Answer

Double bonds are treated as two single bonds to the same atom.

Question 11

Which of the following best describes the difference between cis-trans isomers and enantiomers?

Accepted Answer

Cis-trans isomers are a subtype of diastereomers involving immovable bonds; enantiomers are nonsuperimposable mirror images.

Question 12

A pharmaceutical company produces esomeprazole, the $$(S)$$ enantiomer of omeprazole, for treating acid reflux. Which solution would be optically active?

Accepted Answer

A pure solution of esomeprazole

Question 13

Which of the following molecules will NOT be chiral?

Accepted Answer

A molecule with a plane of symmetry

Question 14

Which of the following is true about diastereomers?

Accepted Answer

They differ at some but not all chiral centers.

Question 15

A cyclohexane ring with two methyl groups on adjacent carbons, both pointing up, is best described as:

Accepted Answer

cis isomer

Question 16

Which of the following manipulations of a Fischer projection will invert the stereochemistry of a chiral center?

Accepted Answer

Switching any two substituents around the chiral center

Question 17

Which of the following best describes the absolute configuration of a chiral center?

Accepted Answer

It is assigned using the Cahn-Ingold-Prelog priority rules.

Question 18

Which of the following is true about the stability of cyclohexane chair conformations with bulky substituents?

Accepted Answer

Bulky groups prefer the equatorial position to minimize nonbonded strain.

Question 19

Which of the following is a correct statement about optical activity?

Accepted Answer

A racemic mixture is optically inactive.

Kaplan Ch 2

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