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

16. Conjugated Systems

Conjugated Hydrohalogenation (1,2 vs 1,4 addition)

Organic Chemistry

16. Conjugated Systems

Conjugated Hydrohalogenation (1,2 vs 1,4 addition)

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8:48 minutes

Problem 36d,e,f

Textbook Question

Would you expect the following nucleophiles to do 1,2- or 1,4-addition?
(d)
(e)
(f)

Verified step by step guidance

Identify the type of nucleophile in each image. The first image shows a nitrogen-based nucleophile, the second image shows an oxygen-based nucleophile with a sodium counterion, and the third image shows a sodium enolate nucleophile.

Understand the concept of 1,2- and 1,4-addition. 1,2-addition involves the nucleophile attacking the carbonyl carbon directly, while 1,4-addition involves the nucleophile attacking the beta carbon in conjugated systems.

Consider the electronic and steric factors. Nitrogen-based nucleophiles are typically more reactive and may favor 1,2-addition due to their ability to attack the carbonyl carbon directly. Oxygen-based nucleophiles, especially enolates, can stabilize through resonance and may favor 1,4-addition.

Analyze the structure of the nucleophiles. The first nucleophile is a tertiary amine, which is less likely to stabilize through resonance and may favor direct attack (1,2-addition). The second nucleophile is a carboxylate ion, which can stabilize through resonance and may favor 1,4-addition. The third nucleophile is an enolate, which is known for 1,4-addition due to resonance stabilization.

Consider the reaction conditions. If the reaction conditions favor kinetic control, 1,2-addition is more likely. If the conditions favor thermodynamic control, 1,4-addition is more likely. This can be influenced by temperature, solvent, and the presence of catalysts.

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Key Concepts

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

Nucleophilicity

Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile, forming a chemical bond. Strong nucleophiles are typically negatively charged or have lone pairs of electrons, making them more reactive. Understanding the strength and nature of nucleophiles is crucial for predicting the type of addition reaction they will undergo, such as 1,2- or 1,4-addition.

1,2- and 1,4-Addition Reactions

1,2- and 1,4-addition reactions describe how nucleophiles add to conjugated systems, such as α,β-unsaturated carbonyl compounds. In 1,2-addition, the nucleophile attacks the carbonyl carbon, while in 1,4-addition, it attacks the β-carbon. The preference for one pathway over the other often depends on the stability of the intermediates and the nature of the nucleophile involved.

Stability of Intermediates

The stability of reaction intermediates plays a significant role in determining the pathway of nucleophilic addition. More stable intermediates, such as resonance-stabilized carbocations, favor certain addition modes. For example, if a nucleophile can stabilize a positive charge through resonance, it may lead to a preference for 1,4-addition, while less stable intermediates may favor 1,2-addition.

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Related Practice

Textbook Question

What are the products of the following reactions, assuming that one equivalent of each reagent is used in each reaction?

Textbook Question

Would you expect the following nucleophiles to do 1,2- or 1,4-addition?

(a)

(b)

Textbook Question

Would you expect the following nucleophiles to do 1,2- or 1,4-addition?a. b. c.

Textbook Question

Would you expect the following nucleophiles to do 1,2- or 1,4-addition?d. e. f.

Textbook Question

Propose a mechanism for each reaction, showing explicitly how the observed mixtures of products are formed.

c. cyclopenta-1,3-diene + Br₂ → 3,4-dibromocyclopent-1-ene + 3,5-dibromocyclopent-1-ene

Textbook Question

When Br₂ is added to buta-1,3-diene at –15 °C, the product mixture contains 60% of product A and 40% of product B. When the same reaction takes place at 60 °C, the product ratio is 10% A and 90% B.

d. If you had a solution of pure A, and its temperature were raised to 60 °C, what would you expect to happen? Propose a mechanism to support your prediction.

Textbook Question

What are the products of the following reactions, assuming that one equivalent of each reagent is used in each reaction? Disregard stereoisomers.

Textbook Question

How many stereoisomers of each product could be obtained?

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