Textbook Question
Indicate whether each pair of Fischer projections represents enantiomers or identical structures.
b.
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20. Carbohydrates
Enantiomers vs Diastereomers
1:53 minutesProblem 17a
Textbook Question
Use the structure of D-galactose in Problem 6.15 to answer the following:
(a) Draw the Fischer projection of the carbon 3 epimer.
Verified step by step guidance1
Understand the concept of epimers: Epimers are stereoisomers that differ in configuration at only one specific carbon atom. In this case, we are focusing on carbon 3 of D-galactose.
Review the Fischer projection of D-galactose: Locate the structure of D-galactose, which is typically represented as a vertical chain with the aldehyde group at the top and hydroxyl groups attached to the carbon atoms.
Identify the hydroxyl group on carbon 3 in D-galactose: In the Fischer projection, determine the orientation (left or right) of the hydroxyl group attached to carbon 3.
Change the configuration at carbon 3: To create the epimer, invert the orientation of the hydroxyl group at carbon 3. If it is on the right in D-galactose, place it on the left, and vice versa.
Redraw the Fischer projection: Update the structure to reflect the new configuration at carbon 3 while keeping the rest of the molecule unchanged. Ensure the aldehyde group remains at the top and the hydroxyl groups on other carbons retain their original orientations.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Fischer Projection
The Fischer projection is a two-dimensional representation of a molecule, particularly useful for depicting the stereochemistry of carbohydrates and amino acids. In this format, the vertical lines represent bonds that are oriented away from the viewer, while horizontal lines indicate bonds that are coming towards the viewer. This method simplifies the visualization of stereoisomers, allowing for easy identification of chiral centers and their configurations.
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0:48
Fischer Projections Example 1
Epimers
Epimers are a specific type of diastereomer that differ in configuration at only one chiral center. In the context of carbohydrates, this means that two sugars can have the same molecular formula and differ only at one specific carbon atom. Understanding epimers is crucial for distinguishing between different forms of sugars, such as d-galactose and d-glucose, which are epimers at carbon 4.
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1:26D vs L Enantiomers Example 2
D-Galactose Structure
D-galactose is a six-carbon aldose sugar that plays a significant role in various biological processes. Its structure includes a chain of carbon atoms with hydroxyl groups (-OH) attached, and it can exist in both linear and cyclic forms. Recognizing the specific arrangement of hydroxyl groups in d-galactose is essential for drawing its Fischer projection and identifying its epimeric forms.
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