Textbook Question
Show how you would synthesize octanal from each compound. You may use any necessary reagents.
(g) ethyl octanoate
7
views
Ch. 18 - Ketones and Aldehydes
Wade9th EditionOrganic ChemistryISBN: 9780135213728
Not the one you use?Change textbookSelect a different textbook
Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 18, Problem 58
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 guidance1
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.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
5mWas this helpful?
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.
Recommended video:
Guided course
07:12
Reductive Amination
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.
Recommended video:
1:38Polymer Stereochemistry Concept 1
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.
Recommended video:
Guided course
02:53Understanding steric effects.
Related Practice
Textbook Question
Show how you would accomplish the following syntheses.
(a) benzene → n-butylbenzene
2
views
Textbook Question
Show how you would synthesize octanal from each compound. You may use any necessary reagents.
(f) octanoic acid
5
views
Textbook Question
Show how you would accomplish the following syntheses.
(b) benzonitrile → propiophenone
4
views
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.
1
views
Textbook Question
Both NaBH4 and NaBD4 are commercially available, and D2O is common and inexpensive. Show how you would synthesize the following labeled compounds, starting with butan-2-one.
(a)
1
views