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.
(b)
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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 80c
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 80cChapter 22, Problem 80c
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.
(c) 
Verified step by step guidance1
Step 1: Recognize that this is a retro-Michael reaction, which involves the reverse of a Michael addition. The reaction occurs under basic conditions (presence of OH⁻) and breaks the bond formed during the original Michael addition.
Step 2: Identify the bond that will be broken. In this case, the bond between the β-carbon of the ketone and the α-carbon of the nitrile group will be cleaved.
Step 3: Under basic conditions, the hydroxide ion (OH⁻) abstracts a proton from the α-carbon of the nitrile group, forming a carbanion at this position.
Step 4: The carbanion then facilitates the cleavage of the bond between the β-carbon of the ketone and the α-carbon of the nitrile group, resulting in the formation of the ketone and the alkene (H₂C=CH-CN).
Step 5: Verify the products formed. The ketone remains intact, and the alkene (H₂C=CH-CN) is generated as a result of the bond cleavage. This completes the retro-Michael reaction mechanism.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Condensation Reactions
Condensation reactions involve the combination of two molecules to form a larger molecule, typically with the loss of a small molecule such as water. These reactions are fundamental in organic chemistry, as they are key in forming complex structures like esters, amides, and polymers. Understanding the conditions and reagents that facilitate these reactions is crucial for predicting the products formed.
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Condensation Reactions
Retro Reactions
Retro reactions, or retro-condensation, refer to the reverse of a condensation reaction, where a larger molecule breaks down into smaller components, often releasing a small molecule like water. This concept is important for understanding the equilibrium between reactants and products in reversible reactions, and it helps in predicting the direction of the reaction under specific conditions.
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Reaction Mechanisms
A reaction mechanism is a step-by-step description of the pathway taken during a chemical reaction, detailing the sequence of bond-breaking and bond-forming events. Understanding mechanisms is essential for predicting the products of a reaction, as well as for designing synthetic routes in organic chemistry. Mechanisms often involve intermediates and transition states that provide insight into the reactivity and stability of the involved species.
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Related Practice
Textbook Question
Show the structure of the compound that results from hydrolysis and decarboxylation of the product.
1
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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)
1
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Textbook Question
Propose a mechanism for the following reaction.
2
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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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Textbook Question
(A true story.) Chemistry lab students added an excess of ethylmagnesium bromide to methyl furoate, expecting the Grignard reagent to add twice and form the tertiary alcohol. After water workup, they found that the product was a mixture of two compounds. One was the expected product having two ethyl groups, but the unexpected product had added three ethyl groups. Propose a mechanism to explain the formation of the unexpected product.
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