Textbook Question
Show how the following compounds can be made using the malonic ester synthesis.
(a) 3-phenylpropanoic acid
(b) 2-methylpropanoic acid
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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 46a,b
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 46a,bChapter 22, Problem 46a,b
Show the resonance forms for the enolate ions that result when the following compounds are treated with a strong base.
(a) ethyl acetoacetate
(b) pentane-2,4-dione
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Identify the alpha-hydrogens in the given compounds. Alpha-hydrogens are the hydrogens attached to the carbon atoms adjacent to the carbonyl group. For (a) ethyl acetoacetate, the alpha-hydrogens are on the methylene group between the two carbonyl groups. For (b) pentane-2,4-dione, the alpha-hydrogens are also on the methylene group between the two carbonyl groups.
When treated with a strong base, the alpha-hydrogens are deprotonated, forming an enolate ion. The enolate ion is stabilized by resonance because the negative charge can be delocalized between the oxygen atom of the carbonyl group and the alpha-carbon.
Draw the first resonance structure of the enolate ion. For (a) ethyl acetoacetate, this involves placing the negative charge on the oxygen atom of one of the carbonyl groups, with a double bond formed between the alpha-carbon and the adjacent carbonyl carbon. For (b) pentane-2,4-dione, follow the same process.
Draw the second resonance structure of the enolate ion. In this structure, the negative charge is delocalized to the alpha-carbon, and the double bond shifts to the oxygen atom of the carbonyl group. This shows the resonance stabilization of the enolate ion.
Verify that the resonance forms are valid by ensuring that the total number of electrons is conserved and that the octet rule is satisfied for all atoms involved. Resonance structures do not represent separate entities but rather a hybrid of all possible forms.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enolate Ion Formation
Enolate ions are formed when a carbonyl compound, such as a ketone or aldehyde, is deprotonated at the alpha carbon by a strong base. This results in a resonance-stabilized anion, where the negative charge can be delocalized between the alpha carbon and the carbonyl oxygen. Understanding this process is crucial for predicting the behavior of compounds like ethyl acetoacetate and pentane-2,4-dione when treated with strong bases.
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Formation of Enolates
Resonance Structures
Resonance structures are different Lewis structures for the same molecule that illustrate the delocalization of electrons. In the case of enolate ions, resonance forms show how the negative charge can be shared between the alpha carbon and the carbonyl oxygen, enhancing the stability of the ion. Recognizing these structures is essential for understanding the reactivity and stability of enolate ions in organic reactions.
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Alpha Carbon Chemistry
The alpha carbon is the carbon atom adjacent to a carbonyl group and plays a significant role in organic reactions, particularly in enolate chemistry. The acidity of the hydrogen atoms on the alpha carbon allows for the formation of enolate ions, which are key intermediates in various reactions, including aldol condensation and Michael addition. A solid grasp of alpha carbon chemistry is necessary to analyze the behavior of compounds like ethyl acetoacetate and pentane-2,4-dione.
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Related Practice
Textbook Question
Show how Claisen condensations could be used to make the following compounds.
(c)
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Textbook Question
Show how Claisen condensations could be used to make the following compounds.
(b)
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Textbook Question
Show the resonance forms for the enolate ions that result when the following compounds are treated with a strong base.
(d) nitroacetone
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Textbook Question
Show the resonance forms for the enolate ions that result when the following compounds are treated with a strong base.
(c) ethyl α-cyanoacetate
Textbook Question
Show how Claisen condensations could be used to make the following compounds.
(d)
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