Question 1

Which of the following statements best explains why humans can digest starch but not cellulose, even though both are composed of glucose units?

Accepted Answer

Starch and cellulose have different types of glycosidic bonds, resulting in different three-dimensional structures.

Question 2

Which of the following pairs are constitutional isomers?

Accepted Answer

2-methylpentane and 3-methylpentane

Question 3

A molecule is chiral if:

Accepted Answer

It is not superimposable on its mirror image.

Question 4

Which of the following molecules is achiral?

Accepted Answer

$$\mathrm{CH_2BrCl}$$

Question 5

How many stereogenic centers are present in 3-bromohexane?

Accepted Answer

1

Question 6

Which of the following statements about enantiomers is correct?

Accepted Answer

They are nonsuperimposable mirror images of each other.

Question 7

Assign the correct R/S configuration to the following stereocenter: a carbon attached to Br, Cl, F, and H, with priorities Br (1), Cl (2), F (3), H (4). If the lowest priority group (H) is in the back and the sequence 1 → 2 → 3 is clockwise, what is the configuration?

Accepted Answer

$$R$$

Question 8

Which of the following best describes a meso compound?

Accepted Answer

An achiral compound that contains stereogenic centers and a plane of symmetry.

Question 9

How many stereoisomers are possible for a molecule with two stereogenic centers, assuming no meso form is possible?

Accepted Answer

$$2^2 = 4$

Question 10

Which of the following statements about optical activity is true?

Accepted Answer

A racemic mixture is optically inactive because the rotations of the two enantiomers cancel each other out.

Question 11

A sample contains 70% of the R enantiomer and 30% of the S enantiomer. What is the enantiomeric excess (ee) of the sample?

Accepted Answer

$$ee = 70\% - 30\% = 40\%$$

Question 12

Which of the following best describes the relationship between cis-1,2-dimethylcyclopentane and trans-1,2-dimethylcyclopentane?

Accepted Answer

They are stereoisomers but not enantiomers.

Question 13

Which of the following is a correct statement about the physical properties of enantiomers?

Accepted Answer

They have identical physical properties except for the direction in which they rotate plane-polarized light.

Question 14

A drug is found to have two enantiomers. One is effective as a pain reliever, while the other is toxic. What is the most likely explanation for this difference?

Accepted Answer

The enantiomers interact differently with chiral biological receptors.

Question 15

Which of the following is true regarding the assignment of R and S configuration to a stereogenic center?

Accepted Answer

The group with the lowest priority should be oriented away from the observer before assigning the configuration.

Question 16

Which of the following statements about diastereomers is correct?

Accepted Answer

Diastereomers are stereoisomers that are not mirror images of each other.

Question 17

Which of the following best describes a plane of symmetry in a molecule?

Accepted Answer

A mirror plane that divides the molecule into two identical halves.

Question 18

Which of the following is a correct statement about the relationship between R/S configuration and optical rotation (+/−)?

Accepted Answer

There is no direct relationship between R/S configuration and the direction of optical rotation.

Question 19

A compound has two stereogenic centers and is found to be achiral. Which of the following best explains this observation?

Accepted Answer

The compound is a meso compound with a plane of symmetry.

Chapter 5 : Stereochemistry: Structure, Isomerism, and Chirality in Organic Molecules

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