Question 1

Which of the following statements best describes a constitutional isomer?

Accepted Answer

Compounds with the same molecular formula but different bond connectivities.

Question 2

Which of the following molecules is chiral?

Accepted Answer

$$\mathrm{CHBrClF}$$

Question 3

A molecule has a single tetrahedral carbon atom bonded to four different groups. Which of the following is true?

Accepted Answer

The molecule is always chiral.

Question 4

Which of the following best describes a meso compound?

Accepted Answer

A compound that is achiral despite having stereogenic centers.

Question 5

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

Accepted Answer

$$4$$

Question 6

Which of the following is true about enantiomers?

Accepted Answer

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

Question 7

A sample of a chiral compound in chloroform (0.500 g/mL) at $$25.0^\circ \mathrm{C}$$ shows an observed rotation of $$+2.5^\circ in a$$ $$1.0$$ decimeter cell. What is the specific rotation $$[\alpha]$$?

Accepted Answer

$$[\alpha] = +5.0$$

Question 8

A mixture contains $$75\% of $$one enantiomer and $$25\% of $$the other. What is the enantiomeric excess (ee)?

Accepted Answer

$$50\%$$

Question 9

Which of the following statements about racemic mixtures is correct?

Accepted Answer

A racemic mixture contains equal amounts of two enantiomers and is optically inactive.

Question 10

Which of the following is the correct relationship between the R/S configuration and optical rotation (+/–)?

Accepted Answer

There is no general relationship between R/S and (+/–); it must be determined experimentally.

Question 11

Which of the following best describes a diastereomer?

Accepted Answer

A stereoisomer that is not a mirror image of another.

Question 12

When assigning priorities for R/S configuration, how are multiple bonds treated?

Accepted Answer

A double bond is treated as if the atom is bonded to two of the same atom.

Question 13

Which of the following is a correct statement about the separation of enantiomers?

Accepted Answer

Enantiomers can be separated by reaction with a chiral reagent to form diastereomers.

Question 14

Which of the following is true about the optical activity of meso compounds?

Accepted Answer

Meso compounds are optically inactive due to an internal plane of symmetry.

Question 15

A compound has two stereogenic centers and a plane of symmetry. How many stereoisomers does it have?

Accepted Answer

$$3$$

Question 16

Which of the following is a real-world example of the importance of chirality in pharmaceuticals?

Accepted Answer

Only one enantiomer of a chiral drug is usually biologically active.

Question 17

Which of the following is the correct formula for calculating enantiomeric excess (ee) from the specific rotation of a mixture and a pure enantiomer?

Accepted Answer

$$ee = \left( \frac{[\alpha]_{	ext{mixture}}}{[\alpha]_{	ext{pure enantiomer}}} ight) 	imes 100$$

Question 18

Which of the following best describes the effect of a racemic mixture on plane-polarized light?

Accepted Answer

It does not rotate plane-polarized light.

Question 19

Which of the following is a correct statement about the number of stereoisomers for a molecule with $$n$$ stereogenic centers and no symmetry?

Accepted Answer

The maximum number of stereoisomers is $$2^n.$$

Question 20

Which of the following is NOT a property of diastereomers?

Accepted Answer

They are mirror images of each other.

Stereochemistry: Chiral Molecules (Chapter 5 Study Notes)

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