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

13. Alcohols and Carbonyl Compounds

Grignard Reaction

Organic Chemistry

13. Alcohols and Carbonyl Compounds

Grignard Reaction

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Problem 45b

Textbook Question

We discuss the reaction of Grignard reagents (organomagnesium compounds) to ketones in Chapter 17. Mechanistically, the reaction proceeds by the nucleophilic addition of a methyl carbanion to the electrophilic carbon of the carbonyl, breaking the C―Oπ bond, resulting in an alkoxide intermediate that is subsequently protonated to produce the 3° alcohol.
(b) Why, when the substrate is modified slightly, does the reaction result in an excess of one stereoisomer?

Verified step by step guidance

Step 1: Understand the basic mechanism of the Grignard reaction. Grignard reagents are organomagnesium compounds that act as nucleophiles. They attack electrophilic carbon atoms, such as those in carbonyl groups, leading to the formation of new carbon-carbon bonds.

Step 2: Recognize the role of stereochemistry in reactions involving chiral centers. When a Grignard reagent reacts with a ketone that has a chiral center, the reaction can produce different stereoisomers depending on the spatial arrangement of the atoms.

Step 3: Consider the concept of stereoselectivity. Stereoselectivity refers to the preference for the formation of one stereoisomer over another in a chemical reaction. This can occur due to steric hindrance or electronic effects that favor the formation of one isomer.

Step 4: Analyze the structure of the substrate. If the substrate has a chiral center or is capable of forming a chiral center during the reaction, the spatial arrangement of substituents can lead to the preferential formation of one stereoisomer.

Step 5: Examine the reaction conditions and the nature of the Grignard reagent. Factors such as the solvent, temperature, and the specific Grignard reagent used can influence the stereoselectivity of the reaction, resulting in an excess of one stereoisomer.

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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 used in organic synthesis to form carbon-carbon bonds. They are highly nucleophilic and react with electrophilic carbon atoms, such as those in carbonyl groups, to form alcohols. The reaction involves the addition of the Grignard reagent to the carbonyl carbon, followed by protonation to yield the final alcohol product.

Stereoisomerism

Stereoisomerism refers to the spatial arrangement of atoms in molecules that have the same molecular formula but differ in the orientation of their atoms in space. This can lead to different physical and chemical properties. In reactions involving chiral centers, such as the addition of Grignard reagents to ketones, the formation of one stereoisomer over another can be influenced by steric and electronic factors.

Nucleophilic Addition Mechanism

The nucleophilic addition mechanism involves the attack of a nucleophile, such as a methyl carbanion from a Grignard reagent, on an electrophilic center, like the carbonyl carbon in ketones. This breaks the C-O π bond, forming an alkoxide intermediate. The intermediate is then protonated to produce an alcohol. The stereochemistry of the product can be affected by the structure of the substrate and the reaction conditions.

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Related Practice

Textbook Question

Show how the reaction of an allylic halide with a Grignard reagent might be used to synthesize the following hydrocarbons.

c. 1-cyclopentylpent-2-ene

Multiple Choice

Predict the major, organic product for the following reaction.

Multiple Choice

Which of the following reactions will NOT produce a 3° alcohol as the major, organic product?

Textbook Question

We discuss the reaction of Grignard reagents (organomagnesium compounds) to ketones in Chapter 17. Mechanistically, the reaction proceeds by the nucleophilic addition of a methyl carbanion to the electrophilic carbon of the carbonyl, breaking the C―Oπ bond, resulting in an alkoxide intermediate that is subsequently protonated to produce the 3° alcohol.

(a) Why does this reaction produce a racemic mixture of 3° alcohols?

Textbook Question

In Chapters 8 and 17 we learn two reactions for the synthesis of the alcohol shown. (a) Show a mechanism for each of the reactions. (b) If you were designing a synthetic route, which would be considered more sustainable? Consider all factors. [Assume the starting organic molecules are equally green.]

Textbook Question

Starting from bromobenzene and any other reagents and solvents you need, show how you would synthesize the following compounds. Any of these products may be used as starting materials in subsequent parts of this problem.

b. 1-phenylpropene

Textbook Question

Which of the following compounds are suitable solvents for Grignard reactions?

(a) n-hexane

(b) CH₃–O–CH₃

(d) cyclohexane

(e) benzene

(f) CH₃OCH₂CH₂OCH₃

(g)

(h)

Textbook Question

Draw the organic products you would expect to isolate from the following reactions (after hydrolysis).