Ch.13 Carbohydrates

Timberlake - Chemistry: An Introduction to General, Organic, and Biological Chemistry 13th Edition

Timberlake13th EditionChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9780134421353Not the one you use?Change textbook

Timberlake 13th Edition

Ch.13 Carbohydrates

Problem 21a

Chapter 13, Problem 21a

Identify each of the following as the D or L enantiomer:
a.

Verified step by step guidance

Step 1: Understand the concept of D and L enantiomers. These are stereoisomers that are mirror images of each other. The D and L notation is based on the orientation of the hydroxyl group (-OH) on the chiral carbon farthest from the carbonyl group in a Fischer projection of the molecule.

Step 2: Examine the Fischer projection of the molecule provided in the image. Identify the chiral carbon farthest from the carbonyl group (C=O). This is typically the second-to-last carbon in the chain for sugars and similar compounds.

Step 3: Determine the position of the hydroxyl group (-OH) attached to this chiral carbon. If the -OH group is on the right side of the Fischer projection, the molecule is classified as the D-enantiomer. If the -OH group is on the left side, it is classified as the L-enantiomer.

Step 4: Verify the orientation of other groups in the molecule to ensure the Fischer projection is correctly interpreted. Remember that the vertical lines represent bonds going away from you (into the plane), and the horizontal lines represent bonds coming toward you (out of the plane).

Step 5: Based on the position of the -OH group on the chiral carbon farthest from the carbonyl group, assign the molecule as either the D or L enantiomer.

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Key Concepts

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

Enantiomers

Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. They have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. This property is crucial in chemistry, particularly in the study of chiral molecules, as enantiomers can exhibit different biological activities and properties.

Chirality

Chirality refers to the geometric property of a molecule that makes it non-superimposable on its mirror image. A chiral molecule typically has at least one carbon atom bonded to four different substituents, creating two distinct forms: the D (dextrorotatory) and L (levorotatory) enantiomers. Understanding chirality is essential for identifying and classifying enantiomers in organic chemistry.

Cahn-Ingold-Prelog Priority Rules

The Cahn-Ingold-Prelog (CIP) priority rules are a set of guidelines used to assign priorities to the substituents attached to a chiral center. By determining the order of priority based on atomic number and connectivity, chemists can establish the configuration of the chiral center as either R (rectus) or S (sinister). This classification is vital for distinguishing between D and L enantiomers in stereochemistry.

Identify each of the following as the D or L enantiomer:a.