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 Configuration

Organic Chemistry

5. Chirality

R and S Configuration

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Problem 60a

Textbook Question

In Chapter 12, we introduce the S_N2 reaction, a nucleophilic substitution reaction that proceeds with inversion. Confirm that inversion has occurred in each of the following examples by determining the absolute configuration of the chiral center in the reactants and products.
(a)

Verified step by step guidance

Step 1: Identify the chiral center in the reactant molecule. The carbon atom bonded to the bromine (Br), hydrogen (H), and two other groups is the chiral center.

Step 2: Assign priorities to the substituents around the chiral center based on the Cahn-Ingold-Prelog rules. Bromine (Br) has the highest priority due to its atomic number, followed by the isopropyl group, the methyl group, and finally hydrogen (H) with the lowest priority.

Step 3: Determine the absolute configuration of the chiral center in the reactant. Arrange the molecule so that the lowest priority group (H) is pointing away from you, then trace the path from the highest priority group to the lowest. If the path is clockwise, the configuration is R; if counterclockwise, it is S.

Step 4: Repeat the process for the product molecule. Assign priorities to the substituents around the chiral center in the product, where the cyanide group (N≡C) replaces bromine. Cyanide has a higher priority than bromine due to its atomic number.

Step 5: Compare the absolute configurations of the reactant and product. If the configuration has changed (e.g., from R to S or vice versa), inversion has occurred, confirming the SN2 reaction mechanism.

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Key Concepts

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

S_N 2 Reaction

The S_N 2 reaction is a type of nucleophilic substitution where a nucleophile attacks an electrophile, resulting in the simultaneous displacement of a leaving group. This reaction is characterized by a single concerted step, leading to the inversion of configuration at the chiral center. The rate of the reaction depends on the concentration of both the nucleophile and the substrate, making it bimolecular.

Inversion of Configuration

Inversion of configuration refers to the change in the spatial arrangement of atoms around a chiral center during a reaction. In S_N 2 reactions, the nucleophile approaches the electrophile from the opposite side of the leaving group, resulting in a switch of the configuration from R to S or vice versa. This is crucial for determining the stereochemical outcome of the reaction.

Absolute Configuration

Absolute configuration describes the specific three-dimensional arrangement of atoms around a chiral center, designated as either R (rectus) or S (sinister) based on the Cahn-Ingold-Prelog priority rules. To confirm inversion in S_N 2 reactions, one must compare the absolute configurations of the reactants and products. This comparison helps in understanding how the stereochemistry is altered during the reaction.

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