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 30a,b

Chapter 5, Problem 30a,b

What is the configuration of the following compounds? (Use the given structures to answer the question.)
a. ( $-$ )-glyceric acid
b. ( $+$ )-isoserine

Verified step by step guidance

Step 1: Identify the chiral center in each compound. Both (-)-glyceric acid and (+)-isoserine have one chiral center, which is the carbon atom bonded to four different groups.

Step 2: Assign priorities to the substituents attached to the chiral center based on the Cahn-Ingold-Prelog priority rules. For (-)-glyceric acid, the groups are COOH, CH2OH, H, and OH. For (+)-isoserine, the groups are COOH, CH2NH3+, H, and OH.

Step 3: Orient the molecule so that the lowest priority group (H) is pointing away from you (on the dashed wedge). This allows you to determine the configuration by tracing the path of the remaining groups in order of priority.

Step 4: Trace the path from the highest priority group to the second and third priority groups. If the path is clockwise, the configuration is R. If the path is counterclockwise, the configuration is S.

Step 5: Use the given labels (-) and (+) to confirm the optical activity of the compounds. (-)-glyceric acid is levorotatory, and (+)-isoserine is dextrorotatory. This does not affect the R/S configuration but provides additional information about the compounds.

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Key Concepts

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

Stereochemistry

Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. It is crucial for understanding the configuration of compounds, particularly in organic chemistry, where the three-dimensional orientation of atoms can lead to different isomers with distinct properties.

Chirality

Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image, much like left and right hands. Chiral molecules often have one or more stereocenters, which are carbon atoms bonded to four different substituents, leading to different configurations known as enantiomers. Understanding chirality is essential for determining the configuration of compounds.

Cahn-Ingold-Prelog Priority Rules

The Cahn-Ingold-Prelog (CIP) priority rules are a set of guidelines used to assign priorities to substituents attached to a stereocenter in order to determine the configuration of chiral centers. By evaluating the atomic number and connectivity of the substituents, chemists can classify the configuration as either R (rectus) or S (sinister), which is vital for accurately describing the stereochemistry of organic compounds.

Related Practice

Textbook Question

a. Is (R)-lactic acid dextrorotatory or levorotatory?

b. Is (R)-sodium lactate dextrorotatory or levorotatory?

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Textbook Question

The reaction of (R)-1-iodo-2-methylbutane with hydroxide ion forms an alcohol without breaking any bonds to the asymmetric center. The alcohol rotates the plane of polarization of plane-polarized light counterclockwise. What is the configuration of (+)-2-methyl-1-butanol?

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Textbook Question

What is the configuration of the following compounds? (Use the given structures to answer the question.)

c. ( $+$ )-lactic acid

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Textbook Question

The observed rotation of 2.0 g of a compound in 50 mL of solution in a polarimeter tube 20 cm long is +138°. What is the specific rotation of the compound?

Convert the Fischer projection to a perspective formula.

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Textbook Question

Draw a perspective formula for each of the following:

a. (S)-2-chlorobutane

b. (R)-1,2-dibromobutane

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