Textbook Question
How many chiral carbon atoms are present in each of the molecules shown in Problem 20.31?
a.
b.
c.
d.
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20. Carbohydrates
Fischer Projections
1:55 minutesProblem 14a
Textbook Question
Draw the Fischer projection for each of the following wedge–dash structures:
a. 
Verified step by step guidance1
Understand the Fischer projection: A Fischer projection is a two-dimensional representation of a molecule where horizontal lines represent bonds projecting out of the plane (toward the viewer) and vertical lines represent bonds projecting into the plane (away from the viewer). The carbon chain is arranged vertically, with the most oxidized carbon (e.g., a carbonyl group) at the top.
Analyze the wedge–dash structure: Identify the chiral center(s) in the given wedge–dash structure. Wedges represent bonds coming out of the plane (toward the viewer), and dashes represent bonds going into the plane (away from the viewer).
Assign the substituents: For each chiral center, determine the four groups attached to it and their spatial arrangement based on the wedge–dash notation.
Convert to Fischer projection: Place the most oxidized carbon at the top of the vertical line. Arrange the substituents such that horizontal bonds (on the Fischer projection) correspond to the wedge bonds (toward the viewer) and vertical bonds correspond to the dash bonds (away from the viewer).
Verify the stereochemistry: Ensure that the stereochemistry (R or S configuration) of the chiral center(s) in the Fischer projection matches the original wedge–dash structure.
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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 three-dimensional organic molecule, particularly useful for depicting carbohydrates and amino acids. In this format, vertical lines represent bonds that extend behind the plane of the paper, while horizontal lines represent bonds that extend in front. This method simplifies the visualization of stereochemistry, allowing for easy identification of chiral centers and their configurations.
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Wedge-Dash Notation
Wedge-dash notation is a way to represent the three-dimensional arrangement of atoms in a molecule. In this notation, solid wedges indicate bonds that project out of the plane towards the viewer, while dashed lines represent bonds that extend behind the plane. This visual tool helps chemists understand the spatial orientation of atoms, which is crucial for determining the molecule's reactivity and interactions.
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Stereochemistry
Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this arrangement affects their chemical properties and reactions. It includes concepts such as chirality, where molecules can exist as non-superimposable mirror images (enantiomers), and geometric isomerism, which involves different spatial arrangements of groups around a double bond. Understanding stereochemistry is essential for predicting the behavior of molecules in biological systems and chemical reactions.
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