Textbook Question
LDA can be used to form enolates on esters and nitriles. Predict the product of these alkylation reactions.
(a)
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24. Enolate Chemistry: Reactions at the Alpha-Carbon
Enolate
5:12 minutesProblem 60g
Textbook Question
For each molecule shown below,
1. indicate the most acidic hydrogens.
2. draw the important resonance contributors of the anion that results from removal of the most acidic hydrogen.
(g) 
Verified step by step guidance1
Step 1: Identify the most acidic hydrogen in the molecule. The molecule contains a carbonyl group (C=O) and an alpha hydrogen adjacent to the carbonyl group. Alpha hydrogens are typically the most acidic due to the resonance stabilization of the resulting enolate ion.
Step 2: Remove the most acidic hydrogen (the alpha hydrogen) to form the conjugate base. This results in the formation of an enolate ion, where the negative charge is delocalized between the alpha carbon and the oxygen atom of the carbonyl group.
Step 3: Draw the first resonance contributor of the enolate ion. In this structure, the negative charge resides on the oxygen atom of the carbonyl group, forming a double bond between the alpha carbon and the carbonyl carbon.
Step 4: Draw the second resonance contributor of the enolate ion. In this structure, the negative charge resides on the alpha carbon, and the carbonyl group retains its double bond.
Step 5: Ensure that both resonance contributors are properly drawn, showing the delocalization of the negative charge between the oxygen atom and the alpha carbon. This resonance stabilization explains the acidity of the alpha hydrogen.
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Video duration:
5mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acidity in Organic Molecules
Acidity in organic chemistry refers to the ability of a molecule to donate a proton (H+). The most acidic hydrogens are typically found on functional groups such as carboxylic acids, alcohols, and phenols. In the provided molecule, the hydrogen attached to the carbon adjacent to the carbonyl group is the most acidic due to the electron-withdrawing effect of the carbonyl, which stabilizes the resulting anion.
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Resonance Structures
Resonance structures are different ways of drawing a molecule that represent the same compound, showing the delocalization of electrons. In the context of the anion formed after deprotonation, resonance contributors illustrate how the negative charge can be distributed across multiple atoms, enhancing the stability of the anion. This concept is crucial for predicting the behavior of the anion in chemical reactions.
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Stability of Anions
The stability of anions is influenced by factors such as electronegativity, resonance, and inductive effects. Anions that can delocalize their negative charge through resonance are generally more stable than those that cannot. In the case of the anion formed from the most acidic hydrogen in the given molecule, resonance with the adjacent carbonyl group significantly stabilizes the anion, making it more favorable for deprotonation.
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