Practice Questions - Isomers - MCAT Organic Chemistry Review

MCAT Organic Chemistry Review

Isomers

Practice Questions

1. Which of the following does NOT show optical activity?

1. (R)-2-butanol

2. (S)-2-butanol

3. A solution containing 1 M (R)-2-butanol and 2 M (S)-2-butanol

4. A solution containing 2 M (R)-2-butanol and 2 M (S)-2-butanol

2. How many stereoisomers exist for the following aldehyde?

1. 2

2. 8

3. 9

4. 16

3. Which of the following compounds is optically inactive?

1.

2.

3.

4.

4. Cholesterol, shown below, contains how many chiral centers?

1. 5

2. 7

3. 8

4. 9

5. Which isomer of the following compound is the most stable?

1.

2.

3.

4. They are all equally stable.

6. The following reaction results in:

1. retention of relative configuration and a change in the absolute configuration.

2. a change in the relative and absolute configurations.

3. retention of the relative and absolute configurations.

4. retention of the absolute configuration and a change in the relative configuration.

7. The following molecules are considered to be:

1. enantiomers.

2. diastereomers.

3. meso compounds.

4. structural isomers.

8. (+)-glyceraldehyde and (–)-glyceraldehyde refer to the (R) and (S) forms of 2,3-dihydroxypropanal, respectively. These molecules are considered:

1. enantiomers.

2. diastereomers.

3. meso compounds.

4. structural isomers.

9. Consider (E)-2-butene and (Z)-2-butene. This is a pair of what type(s) of isomers?

1. Cistrans isomers

2. Diastereomers

3. Enantiomers

1. I only

2. II only

3. I and II only

4. I and III only

10.3-methylpentane and hexane are related in that they are:

1. enantiomers.

2. diastereomers.

3. constitutional isomers.

4. conformational isomers.

11.(R)-2-chloro-(S)-3-bromobutane and (S)-2-chloro-(S)-3-bromobutane are:

1. enantiomers.

2. diastereomers.

3. meso compounds.

4. the same molecule.

12.A scientist takes a 0.5 M solution of an unknown pure dextrorotatory organic molecule and places it in a test tube with a diameter of 1 cm. He observes that a plane of polarized light is rotated 12° under these conditions. What is the specific rotation of this molecule?

1. –240°

2. –24°

3. +24°

4. +240°

13.Omeprazole is a proton pump inhibitor commonly used in gastroesophageal reflux disease. When omeprazole, a racemic mixture, went off-patent, pharmaceutical companies began to manufacture esomeprazole, the (S)-enantiomer of omeprazole, by itself. Given 1 M solutions of omeprazole and esomeprazole, which solution(s) would likely exhibit optical activity?

1. Omeprazole only

2. Esomeprazole only

3. Both omeprazole and esomeprazole

4. Neither omeprazole nor esomeprazole

14.(2R,3S)-2,3-dihydroxybutanedioic acid and (2S,3R)-2,3-dihydroxybutanedioic acid are:

1. meso compounds.

2. the same molecule.

3. enantiomers.

1. I only

2. III only

3. I and II only

4. I and III only

15.If the methyl groups of butane are 120° apart, as seen in a Newman projection, this molecule is in its:

1. highest-energy gauche form.

2. lowest-energy staggered form.

3. middle-energy eclipsed form.

4. highest-energy eclipsed form.

PRACTICE QUESTIONS