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 21

Textbook Question

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

Verified step by step guidance

insert step 1: Understand the difference between 1,2-addition and 1,4-addition. In 1,2-addition, the nucleophile adds to the carbonyl carbon, while in 1,4-addition, the nucleophile adds to the beta carbon of an α,β-unsaturated carbonyl compound.

insert step 2: Identify the type of nucleophile. Strong nucleophiles, such as Grignard reagents or organolithium compounds, typically favor 1,2-addition due to their high reactivity. Weaker nucleophiles, like enolates or amines, may favor 1,4-addition.

insert step 3: Consider the stability of the resulting product. 1,4-addition often leads to more stable products due to the formation of a conjugated system, which can be a driving factor for the reaction pathway.

insert step 4: Evaluate the reaction conditions. Solvent, temperature, and the presence of catalysts can influence whether 1,2- or 1,4-addition is favored.

insert step 5: Apply these considerations to the specific nucleophiles in parts d, e, and f to predict whether they will undergo 1,2- or 1,4-addition.

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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 nucleophile to donate an electron pair to an electrophile during a chemical reaction. Stronger nucleophiles are more likely to participate in reactions, influencing whether they will favor 1,2- or 1,4-addition. Factors affecting nucleophilicity include charge, electronegativity, and solvent effects.

1,2- and 1,4-Addition Mechanisms

1,2- and 1,4-addition mechanisms 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 mechanism over the other can depend on the stability of intermediates and the nature of the nucleophile.

Stability of Intermediates

The stability of reaction intermediates plays a crucial role in determining the pathway of nucleophilic addition. More stable intermediates, such as resonance-stabilized carbocations, favor certain addition modes. Understanding the stability of these intermediates helps predict whether a nucleophile will lead to 1,2- or 1,4-addition in a given reaction.

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Related Practice

Textbook Question

Predict the product of the following addition reactions to dienes.

(a)

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.

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