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

7. Substitution Reactions

Substitution Comparison

Organic Chemistry

7. Substitution Reactions

Substitution Comparison

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3:48 minutes

Problem 14a

Textbook Question

Predict the major products of the following substitutions.
a.

Verified step by step guidance

Identify the type of reaction: Potassium tert-butoxide ((CH3)3CO⁻ K⁺) is a strong, bulky base. This suggests that the reaction will likely proceed via an E2 elimination mechanism rather than a substitution, as bulky bases favor elimination over substitution.

Analyze the substrate: Ethyl bromide (CH3CH2Br) is a primary alkyl halide. Primary alkyl halides typically undergo elimination with strong, bulky bases like tert-butoxide.

Determine the elimination product: In an E2 elimination, the base abstracts a proton (H⁺) from the β-carbon (the carbon adjacent to the carbon bonded to the leaving group, Br⁻). The electrons from the C-H bond form a double bond between the α-carbon (the carbon bonded to the leaving group) and the β-carbon, while the leaving group (Br⁻) departs.

Draw the product: The elimination of HBr from ethyl bromide results in the formation of ethene (CH2=CH2) as the major product. This is because ethene is the simplest alkene that can form from this reaction.

Verify the reaction conditions: Confirm that the reaction conditions (strong, bulky base and primary alkyl halide) are consistent with the E2 mechanism and that no competing SN2 reaction occurs due to steric hindrance from the bulky base.

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Key Concepts

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

Nucleophilic Substitution Reactions

Nucleophilic substitution reactions involve the replacement of a leaving group in a molecule by a nucleophile. In this context, potassium tert-butoxide acts as a strong nucleophile that can attack the electrophilic carbon in ethyl bromide, leading to the formation of a new bond and the release of bromide ion as a leaving group.

Sterics and Nucleophilicity

Sterics refers to the spatial arrangement of atoms in a molecule and can significantly influence reaction pathways. Potassium tert-butoxide is a bulky nucleophile, which favors elimination reactions over substitution due to steric hindrance. Understanding how sterics affects nucleophilicity is crucial for predicting the major products in this reaction.

E2 Elimination Mechanism

The E2 elimination mechanism is a concerted reaction where a base removes a proton from a β-carbon while the leaving group departs from the α-carbon, resulting in the formation of a double bond. In the presence of a strong base like potassium tert-butoxide, the reaction with ethyl bromide is likely to proceed via E2, leading to the formation of an alkene as the major product.

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Draw perspective structures or Fischer projections for the substitution products of the following reactions.

(b)

Textbook Question

a. Optically active 2-bromobutane undergoes racemization on treatment with a solution of KBr. Give a mechanism for this racemization.

b. In contrast, optically active butan-2-ol does not racemize on treatment with a solution of KOH. Explain why a reaction like that in part (a) does not occur.

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Predict the major products of the following substitutions.a.

Key Concepts

Nucleophilic Substitution Reactions

Sterics and Nucleophilicity

E2 Elimination Mechanism

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Predict the major products of the following substitutions.
a.