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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6:25 minutes

Problem 37

Textbook Question

Whereas stabilized enolates do 1,4-addition, unstabilized (normal) enolates can do both 1,2- and 1,4-addition depending on the situation. Why might this be?

Verified step by step guidance

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 position of an α,β-unsaturated carbonyl compound.

Recognize the role of enolates: Enolates are nucleophiles that can attack electrophilic centers. The stability of the enolate affects its reactivity and the type of addition it undergoes.

Consider the stability of enolates: Stabilized enolates, such as those with electron-withdrawing groups, tend to favor 1,4-addition because the resulting product is more stable due to resonance stabilization.

Analyze the reactivity of unstabilized enolates: Unstabilized enolates lack additional stabilizing groups, making them more reactive and capable of undergoing both 1,2- and 1,4-addition. The choice between these pathways depends on reaction conditions and the specific substrate.

Evaluate reaction conditions: Factors such as temperature, solvent, and the presence of catalysts can influence whether an unstabilized enolate undergoes 1,2- or 1,4-addition. Lower temperatures and polar solvents often favor 1,2-addition, while higher temperatures and non-polar solvents can favor 1,4-addition.

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Key Concepts

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

Enolate Formation

Enolates are formed by deprotonation of the alpha hydrogen in carbonyl compounds, resulting in a resonance-stabilized anion. The stability of the enolate is influenced by the substituents on the carbonyl and the solvent used, which affects its reactivity and the type of addition it undergoes.

1,2-Addition vs. 1,4-Addition

1,2-addition involves the nucleophile attacking the carbonyl carbon directly, while 1,4-addition (conjugate addition) involves the nucleophile attacking the beta position of an alpha, beta-unsaturated carbonyl compound. The type of addition is influenced by the stability of the enolate and the reaction conditions.

Stabilized vs. Unstabilized Enolates

Stabilized enolates have additional resonance or inductive stabilization, often due to electron-withdrawing groups, making them favor 1,4-addition. Unstabilized enolates lack such stabilization, allowing them to be more reactive and capable of both 1,2- and 1,4-addition depending on the reaction conditions and the electrophile involved.

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