Question 1

Which of the following statements best describes the difference between chiral and achiral molecules?

Accepted Answer

Chiral molecules are not superimposable on their mirror images, while achiral molecules are superimposable.

Question 2

Which of the following compounds is an example of geometric (cis-trans) isomerism, and what is the biological significance of its isomers?

Accepted Answer

Butenedioic acid; the trans isomer (fumaric acid) is an essential metabolic intermediate, while the cis isomer (maleic acid) is toxic and irritating.

Question 3

Which of the following molecules is chiral?

Accepted Answer

$$\mathrm{CH_3CHBrCH_2CH_3} (2-$$bromobutane)

Question 4

A molecule has a single carbon atom bonded to four different groups. What is this carbon atom called?

Accepted Answer

Chirality center (asymmetric carbon)

Question 5

Which of the following statements about enantiomers is FALSE?

Accepted Answer

Enantiomers have identical interactions with all enzymes in biological systems.

Question 6

Which of the following best describes a racemic mixture?

Accepted Answer

A mixture containing equal amounts of both enantiomers of a chiral compound.

Question 7

A solution of 2.0 g of (+)-glyceraldehyde in 10.0 mL of water was placed in a 100-mm cell. Using the sodium D line, a rotation of $$+1.74^{\circ}$$ was found at $$25^{\circ}C. $$What is the specific rotation $$[\alpha] of (+)-$$glyceraldehyde?

Accepted Answer

$$[\alpha] = +87$$^{\circ}$$

Question 8

Which of the following is NOT a criterion for a carbon atom to be a chirality center?

Accepted Answer

It must be part of a double bond.

Question 9

How many stereoisomers are possible for a molecule with three chirality centers, assuming all centers are different?

Accepted Answer

$$2^3 = 8$

Question 10

Which of the following statements about meso compounds is TRUE?

Accepted Answer

Meso compounds have asymmetric carbon atoms but are achiral due to an internal plane of symmetry.

Question 11

A sample of limonene has an enantiomeric ratio (er) of 97.5:2.5. What is the percent enantiomeric excess (ee)?

Accepted Answer

$$ee = 95\%$$

Question 12

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

Accepted Answer

They are diastereomers.

Question 13

Which of the following is a correct application of the Cahn-Ingold-Prelog priority rules?

Accepted Answer

Assign higher priority to the group with the highest atomic number.

Question 14

Which of the following statements about optical activity is correct?

Accepted Answer

A solution containing only one enantiomer will rotate plane-polarized light.

Question 15

Which of the following best explains why enantiomers can have different biological effects?

Accepted Answer

They interact differently with chiral environments such as enzymes.

Question 16

Which of the following is true about diastereomers?

Accepted Answer

They are stereoisomers that are not mirror images.

Question 17

A solution of 0.50 g of (-)-epinephrine dissolved in 10.0 mL of dilute aqueous HCl was placed in a 20-cm polarimeter tube. Using the sodium D line, the rotation was found to be $$-5.1^{\circ} at$$ $$25^{\circ}C. $$What is the specific rotation $$[\alpha] of $$epinephrine?

Accepted Answer

$$[\alpha] = -102$$^{\circ}$$

Question 18

Which of the following is NOT a property that is identical for a pair of enantiomers?

Accepted Answer

Optical rotation

Question 19

Which of the following best describes the effect of a plane of symmetry on molecular chirality?

Accepted Answer

A molecule with a plane of symmetry is always achiral.

Stereochemistry: Structure, Chirality, and Optical Activity

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