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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 50d
Chapter 5, Problem 50d

Assign the absolute stereochemistry for each of the following molecules drawn in their Fischer projection.
(d)

Verified step by step guidance
1
Step 1: Identify the chiral center in the molecule. In the Fischer projection provided, the carbon atom at the intersection of the vertical and horizontal lines is the chiral center. This carbon is bonded to four different groups: CH₃, OH, H, and a triple bond (C≡C).
Step 2: Assign priorities to the substituents based on the Cahn-Ingold-Prelog (CIP) rules. The priority is determined by atomic number: (1) OH group (oxygen has the highest atomic number), (2) C≡C group (carbon in a triple bond has higher priority than CH₃), (3) CH₃ group, and (4) H (hydrogen has the lowest atomic number).
Step 3: Orient the molecule so that the lowest priority group (H) is pointing away from you. In a Fischer projection, the vertical bonds are considered to be pointing away from the viewer, while the horizontal bonds are pointing toward the viewer. Here, H is already on the vertical axis, so it is pointing away.
Step 4: Determine the order of the remaining groups (OH, C≡C, CH₃) in terms of priority. Trace the path from the highest priority (OH) to the second (C≡C) to the third (CH₃). If the path is clockwise, the configuration is R; if counterclockwise, it is S.
Step 5: Based on the direction of the path traced, assign the absolute stereochemistry (R or S) to the chiral center. Ensure that the lowest priority group (H) is correctly oriented before making the final determination.

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Key Concepts

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

Fischer Projections

Fischer projections are a two-dimensional representation of three-dimensional organic molecules, particularly useful for depicting stereochemistry in carbohydrates and amino acids. In these projections, vertical lines represent bonds that extend away from the viewer, while horizontal lines represent bonds that come towards the viewer. Understanding how to interpret Fischer projections is crucial for assigning stereochemistry accurately.
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Absolute Stereochemistry

Absolute stereochemistry refers to the spatial arrangement of atoms in a molecule and is designated using the R/S system. This system is based on the Cahn-Ingold-Prelog priority rules, which assign priorities to substituents attached to a chiral center. By determining the configuration of the substituents around the chiral center, one can assign either an R (rectus) or S (sinister) designation, which is essential for understanding the molecule's 3D orientation.
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Chirality

Chirality is a property of a molecule that has non-superimposable mirror images, much like left and right hands. A chiral molecule typically contains at least one carbon atom bonded to four different substituents, creating two distinct configurations. Recognizing chirality is fundamental in organic chemistry, as it influences the physical and chemical properties of compounds, including their biological activity.
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Related Practice
Textbook Question

Assign the absolute stereochemistry for each of the following molecules drawn in their Fischer projection.

(a)

1
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Textbook Question

Define the relationship between each set of two molecules as chain isomers, positional isomers, functional group isomers, enantiomers, diastereomers, conformational isomers, or identical

(f)

2
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Textbook Question

Assign the absolute stereochemistry for each of the following molecules.

(e)

1
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Textbook Question

Define the relationship between each set of two molecules as chain isomers, positional isomers, functional group isomers, enantiomers, diastereomers, conformational isomers, or identical

(h)

Textbook Question

Complete the structure of each of these so that it matches the (R) or (S) configuration associated with the name.

(a)

5
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Textbook Question

Assign the absolute stereochemistry for each of the following molecules.

(f)

2
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