Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space

Problem 13

Chapter 5, Problem 13

A molecule of the type shown is discussed in greater detail in Section 6.5.1. Although it contains at least one atom with four different groups attached, why is it not a chiral molecule?

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Step 1: Identify the atom in the molecule that has four different groups attached. In this case, the carbon atom bonded to a hydrogen (H), bromine (Br), and two other groups is the candidate for chirality.

Step 2: Analyze the symmetry of the molecule. A molecule is chiral if it lacks an internal plane of symmetry and cannot be superimposed on its mirror image.

Step 3: Observe the structure of the molecule. The two bromine atoms are positioned symmetrically on opposite sides of the ring, creating an internal plane of symmetry.

Step 4: Determine the impact of the symmetry on chirality. The presence of the internal plane of symmetry means that the molecule is achiral, even though it contains a carbon atom with four different groups attached.

Step 5: Conclude that the molecule is not chiral because the symmetry of the molecule allows it to be superimposed on its mirror image, negating chirality.

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Key Concepts

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

Chirality

Chirality refers to the geometric property of a molecule that makes it non-superimposable on its mirror image. A chiral molecule typically has a carbon atom bonded to four different substituents, resulting in two distinct enantiomers. Understanding chirality is crucial for determining the optical activity of compounds and their interactions in biological systems.

Symmetry

Symmetry in molecules can significantly influence their chirality. A molecule may have a chiral center but can still be achiral if it possesses an internal plane of symmetry. This means that despite having four different groups attached to a central atom, the overall structure can be symmetrical, leading to a lack of chirality.

Stereoisomerism

Stereoisomerism is a form of isomerism where molecules have the same molecular formula and connectivity but differ in the spatial arrangement of atoms. This concept is essential for understanding how different arrangements can lead to chiral or achiral molecules. In the context of the question, recognizing the types of stereoisomers helps clarify why a molecule may not exhibit chirality despite having a chiral center.

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Related Practice

Textbook Question

Identify the following molecules as chiral or achiral. If chiral, draw the nonsuperimposable mirror image and verify its nonsuperimposability.

(c)

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Textbook Question

Identify the following molecules as chiral or achiral. If chiral, draw the nonsuperimposable mirror image and verify its nonsuperimposability.

(e)

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Textbook Question

Draw the mirror image of the following molecule. Then, using the mirror image generated, switch the spatial orientation at the asymmetric center. Is the final structure the enantiomer of the original? If not, what is it?

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Textbook Question

Identify the following molecules as chiral or achiral. If chiral, draw the nonsuperimposable mirror image and verify its nonsuperimposability.

(f)

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Textbook Question

For each of the following chiral molecules, obtain the enantiomer (i) by drawing the nonsuperimposable mirror image and (ii) by switching the spatial orientation at each asymmetric center. Confirm (possibly using models) that the structures you drew for (i) and (ii) are the same.

(b)

Textbook Question

(d)

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