Textbook Question
Show how the amino acid alanine can be synthesized from propanoic acid.
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Ch. 17 - Reactions at the Alpha-Carbon
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
Chapter 18, Problem 76a,b,c
A student tried to prepare the following compounds using aldol condensations. Which of these compounds was she successful in synthesizing? Explain why the other syntheses were not successful.
Verified step by step guidance1
Step 1: Understand the aldol condensation reaction. Aldol condensation involves the reaction of an enolate ion (formed from an aldehyde or ketone) with another carbonyl compound, followed by dehydration to form an α,β-unsaturated carbonyl compound. The reaction requires the presence of α-hydrogens in the starting material.
Step 2: Analyze compound A. Compound A is an α,β-unsaturated aldehyde, which can be successfully synthesized via aldol condensation. The starting materials could be acetaldehyde reacting with itself under basic conditions.
Step 3: Analyze compound B. Compound B is an α,β-unsaturated ketone. This compound can also be synthesized via aldol condensation. The starting materials could be acetone reacting with itself under basic conditions.
Step 4: Analyze compound C. Compound C is an α,β-unsaturated aldehyde with a cyclohexyl group. This compound can be synthesized via aldol condensation using cyclohexanone and acetaldehyde as starting materials. The reaction proceeds successfully because both starting materials have α-hydrogens.
Step 5: Analyze compound D and E. Compound D is an α,β-unsaturated aldehyde with a cyclohexyl group, but it has steric hindrance due to the bulky substituents, making the reaction less favorable. Compound E is an α,β-unsaturated ketone with a branched structure, which may also face steric hindrance or difficulty in enolate formation. These factors could prevent successful synthesis via aldol condensation.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aldol Condensation
Aldol condensation is a reaction between aldehydes or ketones that contain alpha-hydrogens, leading to the formation of β-hydroxy aldehydes or ketones. This reaction involves the nucleophilic addition of an enolate ion to a carbonyl compound, followed by dehydration to form an α,β-unsaturated carbonyl compound. Understanding this mechanism is crucial for predicting which compounds can be synthesized through this method.
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09:51
Crossed Aldol
Enolate Ion Formation
Enolate ions are formed when a base abstracts an alpha-hydrogen from a carbonyl compound, resulting in a resonance-stabilized anion. The stability of the enolate ion is influenced by the structure of the carbonyl compound and the presence of substituents. The ability to form a stable enolate is essential for successful aldol condensation, as it determines the reactivity of the starting materials.
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02:26Formation of Enolates
Steric Hindrance
Steric hindrance refers to the repulsion between bulky groups in a molecule that can impede reactions. In the context of aldol condensation, steric hindrance can affect the accessibility of the carbonyl carbon to nucleophiles, thus influencing the reaction's feasibility. Compounds with significant steric hindrance may not undergo aldol condensation effectively, leading to unsuccessful syntheses.
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02:53Understanding steric effects.
Related Practice
Textbook Question
Show how the following compound can be prepared from starting materials that have no more than five carbons:
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Textbook Question
Show how the following compounds can be synthesized. The only carbon-containing compounds available to you for each synthesis are shown.
b.
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Textbook Question
A Mannich reaction puts a -group on the α-carbon of a ketone. Propose a mechanism for the reaction.
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Textbook Question
A Cannizzaro reaction is the reaction of an aldehyde that has no a-hydrogens with concentrated aqueous sodium hydroxide. In this reaction, half the aldehyde is converted to a carboxylic acid and the other half is converted to an alcohol. Propose a mechanism for the following Cannizzaro reaction:
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Textbook Question
A carboxylic acid is formed when an a-haloketone reacts with hydroxide ion. This reaction is called a Favorskii reaction. Propose a mechanism for the following Favorskii reaction. (Hint: In the first step, HO- removes a proton from the a-carbon that is not bonded to Br; a three-membered ring is formed in the second step; and HO- is a nucleophile in the third step.)
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