Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

5. Chirality

R and S of Fischer Projections

Organic Chemistry

5. Chirality

R and S of Fischer Projections

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2:55 minutes

Problem 19e,f

Textbook Question

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

Verified step by step guidance

Step 1: Identify the asymmetric carbon atoms in each Fischer projection. An asymmetric carbon is a carbon atom bonded to four different groups. In both structures, the two middle carbon atoms are asymmetric.

Step 2: Assign priorities to the substituents around each asymmetric carbon based on the Cahn-Ingold-Prelog (CIP) priority rules. Higher atomic numbers get higher priority. For example, -OH has a higher priority than -H.

Step 3: Determine the configuration (R or S) for each asymmetric carbon. To do this, orient the molecule so that the lowest priority group (usually H) is pointing away from you. Then, trace the path from the highest priority group (1) to the second (2) and third (3). If the path is clockwise, the configuration is (R); if counterclockwise, it is (S).

Step 4: For the first structure, analyze the top asymmetric carbon and assign its configuration (R or S) using the steps above. Repeat the process for the bottom asymmetric carbon.

Step 5: For the second structure, repeat the same process as in Step 4. Assign the configuration (R or S) for the top and bottom asymmetric carbons. Ensure to double-check the orientation of the lowest priority group to avoid errors.

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Key Concepts

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

Fischer Projections

Fischer projections are a two-dimensional representation of three-dimensional organic molecules, particularly useful for depicting stereochemistry. In these diagrams, vertical lines represent bonds that project away from the viewer, while horizontal lines indicate bonds that project towards the viewer. This format is especially helpful for visualizing the configuration of chiral centers in molecules.

Chirality and Asymmetric Carbons

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, or chiral center, is a carbon atom bonded to four different substituents, leading to two possible configurations: (R) for rectus (right) and (S) for sinister (left). Identifying these centers is crucial for understanding the stereochemistry of organic compounds.

Cahn-Ingold-Prelog Priority Rules

The Cahn-Ingold-Prelog (CIP) priority rules are a systematic method for determining the (R) or (S) configuration of 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, guiding the assignment of (R) or (S) based on the spatial arrangement.