Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds

Problem 60a,b,c(2)

Chapter 22, Problem 60a,b,c(2)

For each molecule shown below,
2. draw the important resonance contributors of the anion that results from removal of the most acidic hydrogen.
(a)
(b)
(c)

Verified step by step guidance

Identify the most acidic hydrogen in each molecule. The most acidic hydrogen is typically attached to an atom that can stabilize the resulting negative charge through resonance or electronegativity.

Remove the most acidic hydrogen from each molecule to form the corresponding anion. Represent this step by showing the deprotonation process using curved arrows to indicate the movement of electrons.

Draw the resonance contributors for each anion. Use curved arrows to show the delocalization of the negative charge across the molecule. Focus on atoms with lone pairs, π-bonds, or conjugated systems that can participate in resonance.

Ensure that each resonance structure follows the rules of resonance: (1) the connectivity of atoms remains the same, (2) the total number of electrons does not change, and (3) the octet rule is satisfied wherever possible.

Label the resonance contributors to indicate their relative importance. Typically, resonance structures with full octets, minimal formal charges, and negative charges on more electronegative atoms are more significant.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Resonance Structures

Resonance structures are different Lewis structures for the same molecule that depict the delocalization of electrons. They help illustrate how electrons are distributed across a molecule, particularly in cases where a single Lewis structure cannot fully represent the molecule's behavior. Understanding resonance is crucial for predicting the stability and reactivity of anions formed by deprotonation.

Acidity and pKa

Acidity refers to the tendency of a compound to donate a proton (H+), and it is quantitatively expressed by the pKa value. A lower pKa indicates a stronger acid, meaning the compound more readily loses a proton. Identifying the most acidic hydrogen in a molecule is essential for determining which hydrogen will be removed to form the anion, influencing the resonance contributors of the resulting species.

Anions and Charge Distribution

Anions are negatively charged species formed when a neutral molecule loses a proton. The distribution of charge in an anion can significantly affect its stability and reactivity. Understanding how the charge is delocalized through resonance structures helps in predicting the behavior of the anion and its interactions with other molecules.

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Related Practice

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.

(e)

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Textbook Question

Show how you would use Robinson annulations to synthesize the following compounds. Work backward, remembering that the cyclohexenone is the new ring and that the double bond of the cyclohexenone is formed by the aldol with dehydration. Take apart the double bond, then see what structures the Michael donor and acceptor must have.

(a)

Textbook Question

For each molecule shown below,

1. indicate the most acidic hydrogens.

(a)

(b)

(c)

(b)