Textbook Question
Phenylacetone can form two different enols.
(c) Propose mechanisms for the formation of the first enol in base.
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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 1c2
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 1c2Chapter 22, Problem 1c2
Phenylacetone can form two different enols.
(c) Propose mechanisms for the formation of the second enol in acid.
Verified step by step guidance1
Identify the structure of phenylacetone: It consists of a phenyl group (C₆H₅-) attached to a CH₂ group, which is connected to a carbonyl group (C=O). The carbonyl group is the reactive site for enol formation.
Understand the concept of keto-enol tautomerism: In acidic conditions, the carbonyl compound (phenylacetone) can undergo protonation and rearrangement to form an enol, which is a compound with a hydroxyl group (-OH) attached to a carbon-carbon double bond.
Protonate the carbonyl oxygen: In the presence of an acid, the lone pair of electrons on the oxygen atom of the carbonyl group will accept a proton (H⁺), forming a positively charged oxonium ion (R-C(OH⁺)-R').
Facilitate alpha-hydrogen removal: The acidic environment allows for the removal of an alpha-hydrogen (a hydrogen atom attached to the carbon adjacent to the carbonyl group). This occurs via a resonance-stabilized carbocation intermediate, where the electrons from the C-H bond move to form a double bond between the alpha-carbon and the carbonyl carbon.
Deprotonate the hydroxyl group: A base (such as water) in the solution will remove a proton from the hydroxyl group, resulting in the formation of the enol. The second enol is formed when the alpha-hydrogen on the opposite side of the carbonyl group is removed, leading to a different enol structure.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enol Formation
Enols are compounds with a hydroxyl group (-OH) bonded to a carbon atom that is part of a carbon-carbon double bond. The formation of enols typically involves the tautomerization of carbonyl compounds, where the keto form (C=O) converts to the enol form (C=C-OH). Understanding this process is crucial for analyzing how phenylacetone can yield different enols.
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Formation of Enolates
Acid-Catalyzed Mechanism
In acid-catalyzed reactions, the presence of an acid facilitates the protonation of the carbonyl oxygen, increasing the electrophilicity of the carbonyl carbon. This step is essential for the subsequent nucleophilic attack by water or alcohol, leading to the formation of enols. Recognizing this mechanism is vital for proposing the correct pathway for enol formation in phenylacetone.
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Tautomerization
Tautomerization is a chemical reaction that involves the interconversion between two isomers, typically a keto form and an enol form. This process is often facilitated by acid or base catalysts and is characterized by the migration of a hydrogen atom and a shift in the double bond. Understanding tautomerization is key to explaining how phenylacetone can form two distinct enols under acidic conditions.
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Related Practice
Textbook Question
Phenylacetone can form two different enols.
(c) Propose mechanisms for the formation of the second enol in base.
581
views
Textbook Question
Phenylacetone can form two different enols.
(a) Show the structures of these enols.
(b) Predict which enol will be present in the larger concentration at equilibrium.
940
views
Textbook Question
Phenylacetone can form two different enols.
(c) Propose mechanisms for the formation of the first enol in acid.
887
views