Textbook Question
Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(a) Al3+ vs. B3+
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Ch. 20 - Enolates: Carbonyl Addition and Substitution
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 19, Problem 21a
LDA can be used to form enolates on esters and nitriles. Predict the product of these alkylation reactions.
(a) 
Verified step by step guidance1
Step 1: Identify the role of LDA (Lithium Diisopropylamide). LDA is a strong, non-nucleophilic base commonly used to deprotonate the alpha-hydrogen of carbonyl compounds, forming an enolate intermediate.
Step 2: Locate the alpha-hydrogens in the ester compound. Alpha-hydrogens are the hydrogens attached to the carbon adjacent to the carbonyl group. In this case, the alpha-carbon is the one next to the carbonyl group in the ethyl ester.
Step 3: Deprotonation by LDA. LDA will abstract one of the alpha-hydrogens, forming an enolate ion. The enolate is stabilized by resonance between the oxygen of the carbonyl group and the alpha-carbon.
Step 4: Alkylation reaction. The enolate ion acts as a nucleophile and attacks the electrophilic alkyl halide (ethyl chloride, ClCH2CH3). This results in the formation of a new carbon-carbon bond at the alpha-carbon.
Step 5: Predict the product. The final product will be the ester with an ethyl group added to the alpha-carbon. The structure of the product will reflect the new substitution at the alpha-carbon position.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enolate Formation
Enolates are nucleophilic species formed by the deprotonation of an alpha carbon adjacent to a carbonyl group. In the presence of a strong base like LDA (Lithium diisopropylamide), the hydrogen atom on the alpha carbon is abstracted, resulting in the formation of an enolate ion. This enolate can then act as a nucleophile in subsequent reactions, such as alkylation.
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Formation of Enolates
Alkylation Reactions
Alkylation involves the introduction of an alkyl group into a molecule, typically through a nucleophilic substitution reaction. In this context, the enolate formed from the ester can attack an alkyl halide, such as ethyl chloride, leading to the formation of a new carbon-carbon bond. This process is crucial for building complex organic molecules and expanding carbon skeletons.
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Reactivity of Esters and Nitriles
Esters and nitriles can both undergo enolate formation, but their reactivity differs due to the electronic effects of their functional groups. Esters, with their electron-withdrawing carbonyl, can stabilize the enolate formed, making them suitable substrates for alkylation. Nitriles, while also capable of forming enolates, may exhibit different reactivity patterns due to their triple bond and the nature of the leaving group in alkylation reactions.
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Related Practice
Textbook Question
Rank the reactivity of the following carbonyls with nucleophiles, from least reactive to most reactive.
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Textbook Question
Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(b) Li+ vs. Na+
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Textbook Question
Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(c) Mg2+ vs. Na+
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Textbook Question
Identify the enolate(s) that would form on treatment of each of the following carbonyls with base. [When there are two possibilities, draw both.]
(a)
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