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

Imine vs Enamine

Organic Chemistry

21. Aldehydes and Ketones: Nucleophilic Addition

Imine vs Enamine

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5:14 minutes

Problem 78a

Textbook Question

Propose a mechanism for each of the following reactions:
a.

Verified step by step guidance

Step 1: Analyze the reactants and reagents. The starting material is a molecule containing two ketone groups and an ester functional group. The reagent CH3MgBr is a Grignard reagent, which acts as a nucleophile, and H3O+ is used for acidic workup.

Step 2: Identify the site of nucleophilic attack. The Grignard reagent (CH3MgBr) will attack the carbonyl carbon of the ester group because esters are more reactive towards nucleophiles compared to ketones.

Step 3: Describe the nucleophilic addition. The CH3 group from CH3MgBr will add to the carbonyl carbon of the ester, breaking the C=O bond and forming a tetrahedral intermediate. The ethoxy group (-OCH2CH3) will leave as a leaving group, resulting in a ketone intermediate.

Step 4: Explain the second nucleophilic attack. The Grignard reagent will attack the newly formed ketone group, adding another CH3 group to the carbonyl carbon and forming a tertiary alcohol intermediate.

Step 5: Describe the acidic workup. The H3O+ will protonate the oxygen atoms, stabilizing the molecule and leading to the formation of the final cyclic ketone product and ethanol (CH3CH2OH) as a byproduct.

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Key Concepts

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

Grignard Reagents

Grignard reagents are organomagnesium compounds, typically represented as R-MgX, where R is an organic group and X is a halogen. They are highly reactive nucleophiles that can add to electrophilic carbonyl groups, such as aldehydes and ketones, forming alcohols after hydrolysis. Understanding their reactivity is crucial for proposing mechanisms involving carbonyl compounds.

Nucleophilic Addition Mechanism

The nucleophilic addition mechanism involves the attack of a nucleophile on an electrophilic carbon atom, leading to the formation of a new bond. In the case of Grignard reagents reacting with carbonyl compounds, the nucleophile (Grignard reagent) attacks the carbonyl carbon, resulting in a tetrahedral intermediate. This step is fundamental in understanding how carbonyl compounds are converted into alcohols.

Protonation of Alkoxide

After the nucleophilic addition, the reaction typically involves protonation of the alkoxide intermediate formed. This step is crucial as it converts the alkoxide into a stable alcohol. In the provided reaction, the addition of water (H3O+) serves to protonate the alkoxide, completing the transformation of the carbonyl compound into an alcohol, which is a key outcome of the reaction.

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