Question 1

Which of the following statements best explains why thalidomide caused severe birth defects when administered as a racemic mixture?

Accepted Answer

The R-enantiomer of thalidomide is therapeutically active, while the S-enantiomer is teratogenic.

Question 2

Which of the following molecules is chiral?

Accepted Answer

A tetrahedral carbon atom bonded to four different groups.

Question 3

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

Accepted Answer

$$2^3 = 8$

Question 4

Which of the following best describes a meso compound?

Accepted Answer

A compound with chiral centers that is achiral due to a plane of symmetry.

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

A sample of (±)-2-butanol does not rotate plane-polarized light. What is the best explanation?

Accepted Answer

The sample is a racemic mixture.

Question 7

Which of the following is the correct sequence for assigning R/S configuration using the Cahn-Ingold-Prelog rules?

Accepted Answer

Assign priorities, orient the lowest priority group away, trace from 1→2→3, clockwise is R.

Question 8

Which of the following best describes diastereomers?

Accepted Answer

Stereoisomers that are not mirror images of each other.

Question 9

Which of the following statements about cis- and trans-1,2-dichloroethene is correct?

Accepted Answer

The cis isomer is polar and has a higher boiling point than the trans isomer.

Question 10

Which of the following is NOT a method for resolving a racemic mixture?

Accepted Answer

Simple distillation.

Question 11

A compound has two stereocenters and is found to be optically inactive. Which of the following is the most likely explanation?

Accepted Answer

The compound is a meso compound.

Question 12

Which of the following best describes an epimer?

Accepted Answer

A diastereomer that differs at only one stereocenter.

Question 13

Which of the following is true about the E/Z system for alkenes?

Accepted Answer

E means the highest priority groups are on opposite sides of the double bond.

Question 14

Which of the following molecules would be expected to rotate plane-polarized light?

Accepted Answer

A pure sample of (R)-2-butanol.

Question 15

Which of the following is a constitutional isomer of C$$_4H$_{10}O$$?

Accepted Answer

Butan-1-ol and butan-2-ol

Question 16

Which of the following best explains why enantiomers can have different smells (e.g., carvone in spearmint vs. caraway)?

Accepted Answer

Olfactory receptors are chiral and interact differently with each enantiomer.

Question 17

Which of the following is NOT a characteristic of conformers?

Accepted Answer

They are different compounds that can be separated.

Question 18

Which of the following is true about the D/L system for sugars and amino acids?

Accepted Answer

It is based on the optical rotation of glyceraldehyde.

Question 19

Which of the following is the correct relationship between (2R,3S)-2,3-dibromobutane and (2S,3R)-2,3-dibromobutane?

Accepted Answer

They are enantiomers.

Question 20

Which of the following is NOT true about optical activity?

Accepted Answer

A racemic mixture is optically active.

Stereochemistry and Isomerism: A Comprehensive Study Guide

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