Textbook Question
Which dienophile in each pair is more reactive in a Diels–Alder reaction?
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Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 95e,f
Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 95e,fChapter 9, Problem 95e,f
Protonated cyclohexylamine has a Ka = 1 * 10-11. Using the same sequence of steps as in Problem 94, determine which is a stronger base: cyclohexylamine
or aniline.
e. Which has a greater Ka: cyclohexylammmonium ion or anilinium ion?
f. Which is a stronger acid: cyclohexylamine or aniline?
Verified step by step guidance1
Step 1: Understand the relationship between Ka and acid strength. Ka (acid dissociation constant) measures the strength of an acid. A higher Ka value indicates a stronger acid because it dissociates more in solution.
Step 2: Compare the structures of cyclohexylammonium ion and anilinium ion. Cyclohexylammonium ion is derived from cyclohexylamine, which is an aliphatic amine, while anilinium ion is derived from aniline, which is an aromatic amine. The aromatic ring in aniline can stabilize the positive charge on the conjugate acid (anilinium ion) through resonance.
Step 3: Analyze the conjugate bases. Cyclohexylamine forms a conjugate base (cyclohexylamine) that lacks resonance stabilization, while aniline forms a conjugate base (aniline) that is resonance-stabilized. This stabilization makes aniline a weaker base, and thus its conjugate acid (anilinium ion) is a stronger acid with a higher Ka.
Step 4: Address part (f) by considering the inverse relationship between acid strength and base strength. Cyclohexylamine is a stronger base because it lacks resonance stabilization, making it less likely to donate a proton. Aniline, being resonance-stabilized, is a weaker base and thus a stronger acid.
Step 5: Summarize the findings. For part (e), the anilinium ion has a greater Ka because it is a stronger acid due to resonance stabilization. For part (f), cyclohexylamine is a stronger base, meaning aniline is the stronger acid.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid Dissociation Constant (Ka)
The acid dissociation constant (Ka) quantifies the strength of an acid in solution. It measures the extent to which an acid donates protons (H+) to water, forming its conjugate base. A higher Ka value indicates a stronger acid, as it signifies a greater tendency to lose protons. Understanding Ka is essential for comparing the acidity of different compounds.
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The relationship between equilibrium constant and pKa.
Conjugate Acid-Base Pairs
Conjugate acid-base pairs consist of an acid and its corresponding base that differ by a single proton. When an acid donates a proton, it forms its conjugate base, which can accept a proton back. The stability of the conjugate base influences the strength of the acid; more stable conjugate bases correspond to stronger acids. This concept is crucial for evaluating the relative acidity of cyclohexylamine and aniline.
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Inductive Effect and Resonance
The inductive effect refers to the electron-withdrawing or electron-donating influence of substituents on a molecule, affecting its acidity. Resonance involves the delocalization of electrons across a molecule, stabilizing the conjugate base. In the case of aniline, the amino group can participate in resonance, which affects its acidity compared to cyclohexylamine, where such resonance is absent. Understanding these effects is vital for predicting acid strength.
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01:47Understanding the Inductive Effect.
Related Practice
Textbook Question
Draw the resonance contributors for the phenolate ion.
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Textbook Question
e. Which has a greater Ka: cyclohexanol or phenol?
f. Which is a stronger acid: cyclohexanol or phenol?
Textbook Question
Draw the resonance contributors for phenol.
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Textbook Question
Which dienophile in each pair is more reactive in a Diels–Alder reaction?
1.
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Textbook Question
Draw the major products obtained from the reaction of one equivalent of HBr with the following compounds. For each reaction, indicate the kinetic product and the thermodynamic product.
b.
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