Textbook Question
Propose mechanisms for the following reactions.
(e)
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Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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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
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Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 78c
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 78cChapter 22, Problem 78c
Write equations showing the expected products of the following enamine alkylation and acylation reactions. Then give the final products expected after hydrolysis of the iminium salts.
(c) piperidine enamine of cyclopentanone + methyl iodide
Verified step by step guidance1
Step 1: Recognize that the reaction involves the piperidine enamine of cyclopentanone. An enamine is formed by the reaction of a secondary amine (like piperidine) with a ketone (cyclopentanone). The enamine structure has a double bond adjacent to the nitrogen atom.
Step 2: Understand that the enamine acts as a nucleophile in the alkylation reaction. The double bond in the enamine will attack the electrophilic carbon in methyl iodide (CH₃I), displacing the iodide ion (I⁻) and forming a new carbon-carbon bond.
Step 3: Write the equation for the alkylation reaction. The enamine reacts with methyl iodide to form an intermediate iminium salt. The iminium salt has a positively charged nitrogen atom and a new methyl group attached to the former enamine carbon.
Step 4: Recognize that hydrolysis of the iminium salt regenerates the original ketone structure with the new alkyl group (methyl) added to the alpha-carbon of the ketone. This occurs because water attacks the iminium carbon, leading to the cleavage of the C=N bond and formation of a carbonyl group.
Step 5: Write the final product after hydrolysis. The product is 2-methylcyclopentanone, where the methyl group is attached to the alpha-carbon of the cyclopentanone ring.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enamines
Enamines are derivatives of carbonyl compounds formed by the reaction of an aldehyde or ketone with a secondary amine. They contain a C=C bond adjacent to a nitrogen atom, which makes them nucleophilic and reactive towards electrophiles. In the context of alkylation and acylation, enamines can act as nucleophiles, allowing for the introduction of alkyl or acyl groups to the carbon chain.
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Enamine Mechanism
Iminium Salts
Iminium salts are formed when an enamine reacts with an electrophile, such as an alkyl halide, resulting in the addition of the electrophile to the nitrogen atom. This reaction generates a positively charged nitrogen species, which can be hydrolyzed to yield the corresponding carbonyl compound. Understanding the formation and hydrolysis of iminium salts is crucial for predicting the final products of reactions involving enamines.
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Hydrolysis
Hydrolysis is a chemical reaction involving the breakdown of a compound by water, often resulting in the formation of new products. In the case of iminium salts, hydrolysis leads to the regeneration of the original carbonyl compound and the amine. This step is essential for completing the reaction sequence and understanding the final products formed after the alkylation or acylation of enamines.
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Related Practice
Textbook Question
Write equations showing the expected products of the following enamine alkylation and acylation reactions. Then give the final products expected after hydrolysis of the iminium salts.
(d) piperidine enamine of cyclopentanone + methyl vinyl ketone
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Textbook Question
Write equations showing the expected products of the following enamine alkylation and acylation reactions. Then give the final products expected after hydrolysis of the iminium salts.
(a) pyrrolidine enamine of pentan-3-one + allyl chloride
(b) pyrrolidine enamine of acetophenone + butanoyl chloride
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Textbook Question
Propose mechanisms for the following reactions.
(d)
553
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Textbook Question
Many of the condensations we have studied are reversible. The reverse reactions are often given the prefix retro-, the Latin word meaning “backward.” Propose mechanisms to account for the following reactions.
(a)
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Textbook Question
Show how you would accomplish the following multistep conversions. You may use any additional reagents you need.
(a)
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