Question 1

Which of the following statements best distinguishes constitutional isomers from stereoisomers?

Accepted Answer

Constitutional isomers have the same molecular formula but different connectivity of atoms, while stereoisomers have the same connectivity but differ in spatial arrangement.

Question 2

Which of the following molecules can exhibit cis–trans isomerism?

Accepted Answer

$$\mathrm{CH_3CH=$$CHCH_3$$} (2-$$butene)

Question 3

Which of the following is required for a molecule to be chiral?

Accepted Answer

It must have a carbon atom bonded to four different groups.

Question 4

A sample of lactic acid rotates plane-polarized light to the right. What term describes this property?

Accepted Answer

Dextrorotatory

Question 5

Which of the following compounds is achiral?

Accepted Answer

$$\mathrm{CH_3CH_2CO_2H} ($$propanoic acid)

Question 6

Which of the following best describes a meso compound?

Accepted Answer

A compound with chiral centers and a plane of symmetry, making it optically inactive.

Question 7

How many stereoisomers are possible for a molecule with three chiral centers, assuming no meso forms?

Accepted Answer

$$2^3 = 8$

Question 8

Which of the following statements about enantiomers is FALSE?

Accepted Answer

Enantiomers have different boiling points and melting points.

Question 9

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

Accepted Answer

Iodine (I) has higher priority than bromine (Br) when assigning priorities to substituents on a chiral center.

Question 10

Which of the following best explains why cis–trans isomerism does not occur in 1-butene ($$\mathrm{CH_2$=CHCH_2CH_3}$$)?

Accepted Answer

One of the double-bonded carbons has two identical groups attached.

Question 11

A solution contains a 50:50 mixture of two enantiomers. What is the optical activity of this solution?

Accepted Answer

It is optically inactive (no net rotation).

Question 12

Which of the following is a diastereomer of (2R,3R)-2,3-dibromobutane?

Accepted Answer

(2R,3S)-2,3-dibromobutane

Question 13

Which of the following best describes the difference between a chiral and an achiral molecule?

Accepted Answer

A chiral molecule has a non-superimposable mirror image, while an achiral molecule has a superimposable mirror image.

Question 14

Which of the following real-life examples illustrates the importance of chirality in biological systems?

Accepted Answer

Only L-dopa (not D-dopa) is effective in treating Parkinson’s disease.

Question 15

Which of the following statements about meso compounds is TRUE?

Accepted Answer

Meso compounds are optically inactive despite having chiral centers.

Question 16

Which of the following best describes the effect of light on 11-cis-retinal in the human eye?

Accepted Answer

Light converts 11-cis-retinal to all-trans-retinal, triggering a signal for vision.

Question 17

Which of the following is NOT a property that differs between cis and trans isomers?

Accepted Answer

Molecular formula

Question 18

Which of the following is the maximum number of stereoisomers possible for a molecule with two chiral centers and no plane of symmetry?

Accepted Answer

4

Question 19

Which of the following best describes a racemic mixture?

Accepted Answer

A 1:1 mixture of two enantiomers that is optically inactive.

Isomerism and Stereochemistry: A Biochemistry Study Guide

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