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Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 6 - Stereoisomerism: Arrangement of Atoms in SpaceProblem 24a
Chapter 5, Problem 24a

Prioritize the substituents at each chiral center and then, by comparing them to the models you created in Section 6.3.2, label the absolute configuration as R or S.
(a)

Verified step by step guidance
1
Step 1: Identify the chiral center in the molecule. In this case, the carbon atom bonded to the hydrogen (H), bromine (Br), and the phenyl group (benzene ring) is the chiral center.
Step 2: Assign priorities to the substituents attached to the chiral center based on the Cahn-Ingold-Prelog priority rules. Bromine (Br) has the highest atomic number, so it gets priority 1. The phenyl group is next, as it is a carbon directly bonded to other carbons, so it gets priority 2. The hydrogen (H) has the lowest atomic number, so it gets priority 4.
Step 3: Orient the molecule so that the lowest priority group (hydrogen, priority 4) is pointing away from you (on the dashed wedge). This orientation is crucial for determining the configuration.
Step 4: Trace a path from priority 1 (Br) to priority 2 (phenyl group) to priority 3 (the remaining carbon group). Determine whether this path is clockwise or counterclockwise. Clockwise corresponds to R configuration, and counterclockwise corresponds to S configuration.
Step 5: Compare the result of the path traced to the models in Section 6.3.2 to confirm the absolute configuration as R or S.

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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, much like left and right hands. Chiral centers, typically carbon atoms bonded to four different substituents, are crucial in determining the molecule's stereochemistry. Understanding chirality is essential for labeling configurations as R or S.
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Cahn-Ingold-Prelog Priority Rules

The Cahn-Ingold-Prelog (CIP) priority rules are a set of guidelines used to assign priority to substituents attached to a chiral center. According to these rules, substituents are ranked based on the atomic number of the atoms directly attached to the chiral center, with higher atomic numbers receiving higher priority. This ranking is fundamental for determining the absolute configuration of chiral centers.
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R and S Configuration

The R and S nomenclature is a system used to describe the absolute configuration of chiral centers in molecules. After assigning priorities to the substituents, the configuration is determined by observing the arrangement of the substituents: if the highest priority substituent is positioned clockwise, the configuration is labeled as R (rectus), and if counterclockwise, it is labeled as S (sinister). This labeling is crucial for understanding the stereochemistry of organic compounds.
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Related Practice
Textbook Question

Prioritize the substituents at each chiral center and then, by comparing them to the models you created in Section 6.3.2, label the absolute configuration as R or S.

(d)

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Textbook Question

Of the following pairs, identify the higher priority substituent according to the CIP rules. (R = position of attachment to the asymmetric center.)

(a)

Textbook Question

By comparing them to the models you created in Section 6.3.2, label the following chiral centers as R or S.

(j)

Textbook Question

Order the following sets of substituents via their priority using the CIP rules. (R = position of attachment to the asymmetric center.)

(a)

Textbook Question

Prioritize the substituents at each chiral center and then, by comparing them to the models you created in Section 6.3.2, label the absolute configuration as R or S

(f)

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Textbook Question

Prioritize the substituents at each chiral center and then, by each of the two methods discussed in Section 6.3.2.4, determine the absolute configuration. [Do not use your models, except to check your answers.]

(c)

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