MCAT Organic Chemistry Practice Test 2: Isomers

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

  • A. (R)-2-butanol
  • B. (S)-2-butanol
  • C. A solution containing 1 M (R)-2-butanol and 2 M (S)-2-butanol
  • D. A solution containing 2 M (R)-2-butanol and 2 M (S)-2-butanol

2. How many stereoisomers exist for the following aldehyde?

  • A. 2
  • B. 8
  • C. 9
  • D. 16

3. Which of the following compounds is optically inactive?

  • A.
  • B.
  • C.
  • D.

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

  • A. 5
  • B. 7
  • C. 8
  • D. 9

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

  • A.
  • B.
  • C.
  • D. They are all equally stable.

6. The following reaction results in:

  • A. retention of relative configuration and a change in the absolute configuration.
  • B. a change in the relative and absolute configurations.
  • C. retention of the relative and absolute configurations.
  • D. retention of the absolute configuration and a change in the relative configuration.

7. The following molecules are considered to be:

  • A. enantiomers.
  • B. diastereomers.
  • C. meso compounds.
  • D. structural isomers.

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

  • A. enantiomers.
  • B. diastereomers.
  • C. meso compounds.
  • D. structural isomers.

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

I. Cistrans isomers

II. Diastereomers

III. Enantiomers

  • A. I only
  • B. II only
  • C. I and II only
  • D. I and III only

10. 3-methylpentane and hexane are related in that they are:

  • A. enantiomers.
  • B. diastereomers.
  • C. constitutional isomers.
  • D. conformational isomers.

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

  • A. enantiomers.
  • B. diastereomers.
  • C. meso compounds.
  • D. 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?

  • A. –240°
  • B. –24°
  • C. +24°
  • D. +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?

  • A. Omeprazole only
  • B. Esomeprazole only
  • C. Both omeprazole and esomeprazole
  • D. Neither omeprazole nor esomeprazole

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

I. meso compounds.

II. the same molecule.

III. enantiomers.

  • A. I only
  • B. III only
  • C. I and II only
  • D. 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:

  • A. highest-energy gauche form.
  • B. lowest-energy staggered form.
  • C. middle-energy eclipsed form.
  • D. highest-energy eclipsed form.