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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3:48 minutes

Problem 26a

Textbook Question

A laboratory student added 1-bromobutane to a flask containing dry ether and magnesium turnings. An exothermic reaction resulted, and the ether boiled vigorously for several minutes. Then she added acetone to the reaction mixture and the ether boiled even more vigorously. She added dilute acid to the mixture and separated the layers. She evaporated the ether layer, and distilled a liquid that boiled at 143 °C. GC–MS analysis of the distillate showed one major product with a few minor impurities. The mass spectrum of the major product is shown here.
(a) Draw out the reactions that took place and show the product that was formed.
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Verified step by step guidance

Step 1: Recognize that the reaction involves the preparation of a Grignard reagent. When 1-bromobutane (C4H9Br) reacts with magnesium (Mg) in the presence of dry ether, it forms butylmagnesium bromide (C4H9MgBr). This is a key step in organometallic chemistry.

Step 2: Understand that the Grignard reagent (C4H9MgBr) reacts with acetone (CH3COCH3). The Grignard reagent acts as a nucleophile, attacking the electrophilic carbonyl carbon of acetone. This forms a magnesium alkoxide intermediate.

Step 3: Recognize that the magnesium alkoxide intermediate is then treated with dilute acid (H3O+). This step protonates the alkoxide, converting it into the corresponding alcohol. The product formed is 2-methyl-2-hexanol, a secondary alcohol.

Step 4: Note that the ether layer was evaporated, and the product was distilled. The boiling point of 143 °C suggests that the major product is 2-methyl-2-hexanol, which matches the expected boiling point of this compound.

Step 5: To confirm the product, the mass spectrum analysis shows a major peak corresponding to the molecular ion of 2-methyl-2-hexanol. The fragmentation pattern in the spectrum would also support the structure of this alcohol. Draw the reaction sequence: (1) Formation of C4H9MgBr, (2) Reaction with CH3COCH3, and (3) Protonation to yield 2-methyl-2-hexanol.

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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 formed by the reaction of alkyl or aryl halides with magnesium in dry ether. In this case, 1-bromobutane reacts with magnesium to form butylmagnesium bromide, a highly reactive nucleophile. This reagent can then react with carbonyl compounds, such as acetone, to form alcohols after subsequent acid workup.

Nucleophilic Addition

Nucleophilic addition is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks an electrophilic carbon atom, typically in carbonyl compounds. In this scenario, the butylmagnesium bromide acts as the nucleophile, attacking the carbonyl carbon of acetone, leading to the formation of a tertiary alcohol after protonation with dilute acid.

Distillation and GC-MS Analysis

Distillation is a separation technique used to purify liquids based on differences in boiling points. In this experiment, the ether layer is evaporated, and the distillate is analyzed using Gas Chromatography-Mass Spectrometry (GC-MS), which provides information about the composition and structure of the major product and any impurities present. The boiling point of the distillate at 143 °C suggests the formation of a specific tertiary alcohol from the reaction.

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Related Practice

Textbook Question

Show how you would synthesize the following compound from alkyl halides, vinyl halides, and aryl halides containing no more than six carbon atoms.

(a) octane

Textbook Question

Predict the major products of the following reactions, including stereochemistry where appropriate.

(h) cyclooctylmethanol + CH₃CH₂MgBr

(i) potassium tert-butoxide + methyl iodide

(j) sodium methoxide + tert-butyl iodide

Textbook Question

Which of the following alkyl halides could be successfully used to form a Grignard reagent?

Textbook Question

How could the following compounds be prepared, using cyclohexene as a starting material?

Textbook Question

Starting with cyclohexane, how could the following compounds be prepared?

Textbook Question

A chemist attempted the reaction below, one we introduce in Chapter 17, expecting the reaction between a strong nucleophile and a ketone in water to give an alkoxide product.

(a) Why did the reaction fail?

(b) How could the reaction conditions be changed to give a successful reaction?

Textbook Question

Give the expected products of the following reactions. Include a protonation step where necessary.

(a) 2,2-dimethyloxirane + isopropylmagnesium bromide

(b) propylene oxide + n-butyllithium

Textbook Question

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