Textbook Question
Identify A–C. (Hint: A shows three singlets in its 1H NMR spectrum with integral ratios 3 : 2 : 3 and gives a positive iodoform test; see Problem 58.)
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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 57
An aldol addition can be catalyzed by acids as well as by bases. Propose a mechanism for the acid-catalyzed aldol addition of propanal.
Verified step by step guidance1
Step 1: Begin by protonating the carbonyl oxygen of propanal using an acid catalyst. This increases the electrophilicity of the carbonyl carbon, making it more susceptible to nucleophilic attack. The protonation can be represented as:
Step 2: The alpha hydrogen of propanal becomes more acidic due to the protonation of the carbonyl group. Remove the alpha hydrogen using a weak base (such as water), forming an enol intermediate. The enol structure can be represented as:
Step 3: The enol intermediate acts as a nucleophile and attacks the protonated carbonyl group of another propanal molecule. This step forms a new C-C bond between the alpha carbon of the enol and the carbonyl carbon of the second propanal molecule.
Step 4: After the nucleophilic attack, the intermediate formed undergoes deprotonation to stabilize the molecule. This results in the formation of a beta-hydroxy aldehyde, which is the product of the aldol addition reaction.
Step 5: Finally, regenerate the acid catalyst by transferring a proton from the intermediate to the solvent or another molecule in the reaction mixture. This ensures the catalyst is available for further reactions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aldol Addition
Aldol addition is a reaction between two carbonyl compounds, typically aldehydes or ketones, that results in the formation of a β-hydroxy carbonyl compound. This reaction involves the nucleophilic attack of an enolate ion on another carbonyl carbon, leading to the formation of a new carbon-carbon bond. The aldol product can further undergo dehydration to yield an α,β-unsaturated carbonyl compound.
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Acid Catalysis
Acid catalysis involves the use of an acid to increase the rate of a chemical reaction. In the context of aldol addition, the acid protonates the carbonyl oxygen, enhancing the electrophilicity of the carbonyl carbon. This makes it more susceptible to nucleophilic attack by the enolate ion, facilitating the formation of the aldol product.
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Mechanism of Aldol Addition
The mechanism of acid-catalyzed aldol addition begins with the protonation of the carbonyl oxygen, followed by the formation of an enol or enolate ion from another molecule of the aldehyde. The enolate then attacks the protonated carbonyl carbon, leading to the formation of the β-hydroxy carbonyl compound. This mechanism highlights the role of acid in stabilizing intermediates and promoting the reaction pathway.
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Related Practice
Textbook Question
Using cyclopentanone as the reactant, show the product of
b. an aldol addition.
c. an aldol condensation.
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Textbook Question
Draw the products of the following reactions:
a.
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Textbook Question
Draw the products of the following reactions:
d. diethyl 1,2-benzenedicarboxylate + sodium ethoxide: (1) slow addition of ethyl acetate; (2) HCl
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Textbook Question
Draw the products of the following reactions:
b.
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Textbook Question
In the presence of excess base and excess halogen, a methyl ketone is converted to a carboxylate ion. The reaction is known as the haloform reaction because one of the products is haloform (chloroform, bromoform, or iodoform). Before spectroscopy became a routine analytical tool, the haloform reaction served as a test for methyl ketones: the formation of iodoform, a bright yellow compound, signaled that a methyl ketone was present. Why do only methyl ketones form a haloform?
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