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

21. Aldehydes and Ketones: Nucleophilic Addition

Wittig Reaction

Organic Chemistry

21. Aldehydes and Ketones: Nucleophilic Addition

Wittig Reaction

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3:55 minutes

Problem 51e

Textbook Question

Show how you would accomplish the following syntheses efficiently and in good yield. You may use any necessary reagents.
(e)

Verified step by step guidance

Step 1: Analyze the transformation. The starting material is a cyclopentanone with an aldehyde group at the beta position. The product introduces an ethyl group at the alpha position of the ketone, forming an α,β-unsaturated aldehyde.

Step 2: Perform an α-alkylation reaction. Treat the cyclopentanone with a strong base, such as LDA (lithium diisopropylamide), to generate the enolate ion. This enolate is nucleophilic at the alpha position.

Step 3: Introduce the ethyl group. React the enolate with ethyl bromide (CH3CH2Br) or ethyl iodide (CH3CH2I) in an SN2 reaction to alkylate the alpha position of the ketone.

Step 4: Perform an aldol condensation. Treat the α-ethyl cyclopentanone with a base, such as NaOH or KOH, to form an enolate at the alpha position. This enolate will attack the aldehyde group intramolecularly, forming a β-hydroxy ketone intermediate.

Step 5: Dehydrate the β-hydroxy ketone. Heat the intermediate under acidic or basic conditions to eliminate water and form the α,β-unsaturated aldehyde product.

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Key Concepts

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

Reaction Mechanisms

Understanding reaction mechanisms is crucial in organic chemistry as it describes the step-by-step process by which reactants transform into products. This includes identifying intermediates, transition states, and the role of catalysts. A clear grasp of mechanisms helps predict the outcome of reactions and optimize conditions for better yields.

Reagents and Conditions

The choice of reagents and reaction conditions significantly influences the efficiency and yield of a synthesis. Different reagents can provide specific functional groups or facilitate particular reaction pathways. Additionally, factors such as temperature, pressure, and solvent can affect reaction rates and selectivity, making it essential to select the right conditions for the desired outcome.

Yield and Efficiency

Yield refers to the amount of product obtained from a reaction compared to the theoretical maximum, while efficiency encompasses both yield and the time and resources used. High yield and efficiency are desirable in synthetic chemistry, as they indicate a successful reaction with minimal waste. Understanding how to maximize these factors is key to effective synthesis.

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Related Practice

Textbook Question

Propose mechanisms for the following reactions.

(c)

Textbook Question

The Wittig reaction is useful for placing double bonds in less stable positions. For example, the following transformation is easily accomplished using a Wittig reaction.

(a) Show how you would use a Wittig reaction to do this.

(b) Show how you might do this without using a Wittig reaction, and then explain why the Wittig reaction is a much better synthesis.

Textbook Question

Like other strong nucleophiles, triphenylphosphine attacks and opens epoxides. The initial product (a betaine) quickly cyclizes to an oxaphosphetane that collapses to an alkene and triphenylphosphine oxide.

(a) Show each step in the reaction of trans-2,3-epoxybutane with triphenylphosphine to give but-2-ene. What is the stereochemistry of the double bond in the product?

Textbook Question

(b) Show how this sequence might be used to convert cis-cyclooctene to trans-cyclooctene.

Textbook Question

Show how you would accomplish the following synthetic conversions efficiently and in good yield. You may use any necessary additional reagents and solvents.

(h)

Textbook Question

What two sets of reagents (each consisting of a carbonyl compound and phosphonium ylide) can be used for the synthesis of the following alkene?

Textbook Question

Suggest the appropriate carbonyl and Wittig reagent to make the following alkenes.

a. (E)-7-methylnon-4-en-3-one

Multiple Choice

Determine the carbonyl and ylide that formed the following product.

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Show how you would accomplish the following syntheses efficiently and in good yield. You may use any necessary reagents.(e)

Key Concepts

Reaction Mechanisms

Reagents and Conditions

Yield and Efficiency

Watch next

Show how you would accomplish the following syntheses efficiently and in good yield. You may use any necessary reagents.
(e)