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

Reducing Agent

Organic Chemistry

13. Alcohols and Carbonyl Compounds

Reducing Agent

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5:12 minutes

Problem 58

Textbook Question

When LiAlH₄ reduces 3-methylcyclopentanone, the product mixture contains 60% cis-3-methylcyclopentanol and 40% trans-3-methylcyclopentanol. Use your models, and make three-dimensional drawings to explain this preference for the cis isomer.

Verified step by step guidance

Understand the reaction: Lithium aluminum hydride (LiAlH4) is a strong reducing agent that reduces ketones, such as 3-methylcyclopentanone, to their corresponding alcohols. The reduction occurs via a nucleophilic attack of the hydride ion (H⁻) on the carbonyl carbon.

Analyze the stereochemistry of the starting material: 3-methylcyclopentanone is a cyclic ketone with a methyl group at the 3-position. The carbonyl group is planar (sp² hybridized), allowing the hydride to attack from either the top face or the bottom face of the molecule.

Consider the steric effects during the hydride attack: The methyl group at the 3-position creates steric hindrance. When the hydride attacks from the same face as the methyl group, the resulting alcohol will have the methyl and hydroxyl groups in a cis configuration. When the hydride attacks from the opposite face, the product will have a trans configuration.

Explain the preference for the cis isomer: The cis isomer is favored because the transition state for hydride attack on the same face as the methyl group is less sterically hindered. In the trans configuration, the bulky methyl and hydroxyl groups are on opposite sides, leading to greater steric strain in the transition state.

Summarize the product distribution: The reaction produces a mixture of cis-3-methylcyclopentanol (60%) and trans-3-methylcyclopentanol (40%) due to the steric preference for the cis isomer during the reduction process. This preference is a result of the lower steric hindrance in the transition state leading to the cis product.

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Key Concepts

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

Reduction Reactions

Reduction reactions involve the gain of electrons or hydrogen, or the loss of oxygen. In organic chemistry, reducing agents like lithium aluminum hydride (LiAlH4) are used to convert carbonyl compounds, such as ketones, into alcohols. Understanding the mechanism of reduction is crucial for predicting the products formed during the reaction.

Stereochemistry

Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the case of 3-methylcyclopentanone reduction, the formation of cis and trans isomers is influenced by the steric and electronic interactions during the reaction. Recognizing the differences between these isomers helps explain the observed product distribution.

Steric Hindrance

Steric hindrance refers to the repulsion between bulky groups in a molecule that can affect the reactivity and stability of intermediates. In the reduction of 3-methylcyclopentanone, the steric environment around the cyclopentane ring influences the formation of the cis isomer, which is favored due to less steric strain compared to the trans isomer. This concept is essential for understanding why certain isomers are produced preferentially.

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Related Practice

Textbook Question

What products are obtained from the reaction of the following compounds with LiAlH₄ followed by treatment with dilute acid?

c. methyl benzoate

d. pentanoic acid

Textbook Question

What amides would you react with LiAlH₄ to form the following amines?

a. benzylmethylamine

b. ethylamine

c. diethylamine

d. triethylamine

Textbook Question

An unknown alcohol with a molecular formula of C₇H₁₄O was oxidized to an aldehyde with HOCl. When an acidic solution of the alcohol was distilled, two alkenes were obtained. The alkene formed in greater yield was determined to be 1-methylcyclohexene. The other alkene formed the original un-known alcohol when treated with BH₃/THF followed by H₂O₂, HO^-, and H₂O. Identify the unknown alcohol.

Textbook Question

Compounds containing deuterium (D = ²H) are useful for kinetic studies and metabolic studies with new pharmaceuticals. One way to introduce deuterium is by using the reagent LiAlD₄, equivalent in reactivity to LiAlH₄. Show how to make these deuterium-labeled compounds, using LiAlD₄ and D₂O as your sources of deuterium, and any non-deuterated starting materials you wish.

(b) CH₃CD₂OH

Textbook Question

In which step(s) of the hydride reduction of an ester does the compound undergo reduction? (Hint: Count the bonds to oxygen.)

Textbook Question

Propose a mechanism for the reduction of octanoyl chloride by lithium aluminum hydride.

Textbook Question

Show how you would synthesize each compound, starting with an ester containing no more than eight carbon atoms. Any other necessary reagents may be used.

(d) Ph₂CHOH

(e) PhCH₂OH

(f) PhCOOH

Textbook Question

Show how you would synthesize the following alcohol by reducing appropriate carbonyl compound.

(d)

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