Textbook Question
The following compounds can all react as bases.
c. Rank the original compounds in order, from strongest base to weakest base.
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Ch. 2 - Acids and Bases; Functional Groups
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
Chapter 2, Problem 48
Consider the following compounds that vary from nearly nonacidic to strongly acidic. Draw the conjugate bases of these compounds, and explain why the acidity increases so dramatically with substitution by nitro groups.
Verified step by step guidance1
Step 1: Understand the concept of conjugate bases. A conjugate base is formed when an acid donates a proton (H⁺). The strength of an acid is inversely related to the stability of its conjugate base.
Step 2: Draw the conjugate base for each compound. For CH₄, remove an H⁺ to form CH₃⁻. For CH₃NO₂, remove an H⁺ from the carbon to form CH₂NO₂⁻. For CH₂(NO₂)₂, remove an H⁺ from the carbon to form CH(NO₂)₂⁻. For CH(NO₂)₃, remove an H⁺ from the carbon to form C(NO₂)₃⁻.
Step 3: Analyze the effect of nitro groups on acidity. Nitro groups are electron-withdrawing due to their strong electronegativity and resonance stabilization. This increases the stability of the conjugate base by delocalizing the negative charge.
Step 4: Compare the stability of the conjugate bases. As more nitro groups are added, the conjugate base becomes more stable due to increased resonance and inductive effects, making the original compound more acidic.
Step 5: Relate pKa values to acidity. Lower pKa values indicate stronger acids. The dramatic decrease in pKa from CH₄ to CH(NO₂)₃ reflects the increased acidity due to the stabilizing effect of multiple nitro groups on the conjugate base.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Conjugate Base
A conjugate base is formed when an acid donates a proton (H+). It is the species that remains after the acid has lost a proton. Understanding the stability of conjugate bases is crucial, as more stable conjugate bases correspond to stronger acids. Stability can be influenced by factors such as resonance and electronegativity.
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Conjugated states
pKa and Acidity
The pKa value is a measure of the acidity of a compound, indicating how easily it can donate a proton. Lower pKa values correspond to stronger acids. The dramatic decrease in pKa values with the addition of nitro groups suggests increased acidity, which is often due to the stabilization of the conjugate base through resonance and electron-withdrawing effects.
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Electron-Withdrawing Groups
Electron-withdrawing groups, such as nitro groups, increase acidity by stabilizing the conjugate base. They achieve this by delocalizing negative charge through resonance or inductive effects, making the conjugate base more stable. The presence of multiple nitro groups enhances this effect, leading to a significant increase in acidity.
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Related Practice
Textbook Question
Methyllithium (CH3Li) is often used as a base in organic reactions.
b. What is the conjugate acid of CH3Li? Would you expect CH3Li to be a strong base or a weak base?
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Textbook Question
The following compounds can all react as acids.
a. For each compound, show its conjugate base. Show any resonance forms if applicable.
Textbook Question
Label the reactants in these acid–base reactions as Lewis acids (electrophiles) or Lewis bases (nucleophiles). Use curved arrows to show the movement of electron pairs in the reactions.
(b)
Textbook Question
The following compounds can all react as acids.
b. Rank the conjugate bases in the order you would predict, from most stable to least stable.
Textbook Question
Label the reactants in these acid–base reactions as Lewis acids (electrophiles) or Lewis bases (nucleophiles). Use curved arrows to show the movement of electron pairs in the reactions.
(a)