Ch. 4 - Isomers: The Arrangement of Atoms in Space

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 4 - Isomers: The Arrangement of Atoms in Space

Problem 74

Chapter 5, Problem 74

Which of the following are optically active?

Verified step by step guidance

Step 1: Understand the concept of optical activity. A molecule is optically active if it has a chiral center and lacks a plane of symmetry. A chiral center is a carbon atom bonded to four different groups.

Step 2: Analyze structure (a). The carbon atom bonded to OH, Cl, and two different groups from the cyclobutane ring is a chiral center. This structure lacks symmetry, making it optically active.

Step 3: Analyze structure (b). The carbon atom bonded to OH and Cl is not a chiral center because the cyclobutane ring provides two identical groups. This structure is not optically active.

Step 4: Analyze structure (c). The carbon atom bonded to OH, Cl, and two different groups from the cyclobutane ring is a chiral center. This structure lacks symmetry, making it optically active.

Step 5: Analyze structure (d). The carbon atom bonded to OH and Cl is not a chiral center because the cyclobutane ring provides two identical groups. This structure is not optically active.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Optical Activity

Optical activity refers to the ability of a chiral molecule to rotate the plane of polarized light. This property arises from the presence of a chiral center, typically a carbon atom bonded to four different substituents, leading to non-superimposable mirror images known as enantiomers. Only chiral compounds exhibit optical activity, making this concept crucial for identifying optically active substances.

Chirality

Chirality is a geometric property of some molecules that makes them non-superimposable on their mirror images. A chiral molecule usually contains at least one carbon atom bonded to four distinct groups, creating two enantiomers. Understanding chirality is essential for determining whether a compound is optically active, as only chiral molecules can exhibit this property.

Stereoisomers

Stereoisomers are compounds that have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. This category includes enantiomers, which are mirror images of each other, and diastereomers, which are not. Recognizing the types of stereoisomers is important for assessing optical activity, as only enantiomers are optically active.

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Determining when molecules are stereoisomers.

Related Practice

Textbook Question

Assign relative priorities to each set of substituents:

c. -C(=O)CH₃, -CH=CH₂, -Cl, -C=N

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Textbook Question

Draw the structure for a compound with molecular formula C₂H₂I₂F₂

c. that is optically active.

Textbook Question

Draw the structure for a compound with molecular formula C₂H₂I₂F₂

a. that is optically inactive because it does not have an asymmetric center.

b. that is optically inactive because it is a meso compound.

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Textbook Question

For many centuries, the Chinese have used extracts from a group of herbs known as ephedra to treat asthma. A compound named ephedrine has been isolated from these herbs and found to be a potent dilator of air passages in the lungs.

a. How many stereoisomers does ephedrine have?

b. The stereoisomer shown here is the one that is pharmacologically active. What is the configuration of each of the asymmetric centers?

Name the following:

Which of the following has an achiral stereoisomer?

a. 2,3-dichlorobutane

b. 2,3-dichloropentane

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