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Ch.5 - Stereochemistry
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Non è quello che usi tu?Cambia libro di testo
Capitolo 5, Problema 19c,d

For each Fischer projection, label each asymmetric carbon atom as (R) or (S).
(c)
(d)

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1
Step 1: Identify the chiral centers in each Fischer projection. A chiral center is a carbon atom bonded to four different groups. For structure (c), the central carbon is a chiral center. For structure (d), the two middle carbons are chiral centers.
Step 2: Assign priorities to the substituents attached to each chiral center based on the Cahn-Ingold-Prelog (CIP) priority rules. Higher atomic numbers get higher priority. For example, in (c), Br > CH2Br > CH3 > H. In (d), prioritize CHO > OH > CH2OH > H for the top chiral center, and OH > CH2OH > H > H for the bottom chiral center.
Step 3: Orient the Fischer projection so that the lowest priority group (usually H) is pointing away from you (on the vertical axis). If the lowest priority group is not already on the vertical axis, mentally rotate the molecule to achieve this orientation.
Step 4: Determine the sequence of the remaining three groups (1 → 2 → 3) in a clockwise or counterclockwise direction. If the sequence is clockwise, the configuration is (R). If it is counterclockwise, the configuration is (S).
Step 5: Label each chiral center in (c) and (d) as (R) or (S) based on the analysis in Step 4. Ensure to double-check the orientation and priority assignments for accuracy.

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Fischer Projections

Fischer projections are a two-dimensional representation of three-dimensional organic molecules, particularly useful for depicting stereochemistry. In these projections, vertical lines represent bonds that extend away from the viewer, while horizontal lines represent bonds that come towards the viewer. This format helps in identifying the configuration of chiral centers in molecules.
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Chirality and Asymmetric Carbon Atoms

Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image, often due to the presence of asymmetric carbon atoms. An asymmetric carbon atom is one that is bonded to four different substituents, leading to two possible configurations: (R) for rectus (right) and (S) for sinister (left). Identifying these configurations is crucial for understanding the stereochemistry of organic compounds.
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Cahn-Ingold-Prelog Priority Rules

The Cahn-Ingold-Prelog (CIP) priority rules are a set of guidelines used to assign (R) or (S) configurations to chiral centers. According to these rules, substituents attached to the chiral carbon are ranked based on atomic number, with higher atomic numbers receiving higher priority. If two substituents have the same atomic number, the next atoms in the substituent chain are compared until a difference is found.
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