Textbook Question
Which is a stronger base: ethoxide ion or acetate ion? Give pKb values (without looking them up) to support your choice.
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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 21a,b,c
Choose the more acidic member of each pair of isomers, and show why the acid you chose is more acidic.
(a) 
(b) 
(c) 
Verified step by step guidance1
Identify the functional groups present in each compound. For pair (b), both compounds are carboxylic acids with a cyclohexene ring. For pair (c), both compounds are phenols with a fluorine substituent.
Consider the effect of resonance on acidity. In pair (b), the presence of a double bond in the cyclohexene ring can affect the resonance stabilization of the carboxylate ion formed after deprotonation.
Analyze the inductive effect in pair (c). The fluorine atom is highly electronegative and can withdraw electron density through the sigma bonds, stabilizing the negative charge on the phenoxide ion after deprotonation.
Compare the resonance stabilization in pair (b). The compound with the double bond closer to the carboxyl group may have better resonance stabilization, making it more acidic.
Evaluate the position of the fluorine atom in pair (c). The position of the fluorine relative to the hydroxyl group can influence the acidity due to the inductive effect. The closer the fluorine is to the hydroxyl group, the more it can stabilize the negative charge on the phenoxide ion.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acidity and pKa
Acidity in organic chemistry refers to the ability of a compound to donate a proton (H+). The strength of an acid is often measured by its pKa value; lower pKa values indicate stronger acids. Understanding the relationship between structure and acidity is crucial, as factors like electronegativity and resonance can significantly influence a compound's ability to stabilize the negative charge of its conjugate base.
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07:45
Identifying pKa values
Resonance Stabilization
Resonance stabilization occurs when a molecule can be represented by two or more valid Lewis structures, allowing for the delocalization of electrons. This delocalization can stabilize the conjugate base formed after deprotonation, making the original acid stronger. In the context of isomers, the presence of resonance structures can help determine which isomer is more acidic based on the stability of its conjugate base.
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03:43The radical stability trend.
Inductive Effect
The inductive effect refers to the electron-withdrawing or electron-donating effects transmitted through sigma bonds in a molecule. Electronegative atoms or groups can stabilize a negative charge on a conjugate base by pulling electron density away, enhancing acidity. When comparing isomers, the presence of electronegative substituents can significantly influence their relative acidity by affecting the stability of the conjugate base.
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01:47Understanding the Inductive Effect.
Related Practice
Textbook Question
Acetic acid can also react as a very weak base (pKb = 20). Two different sites on acetic acid might become protonated to give the conjugate acid. Draw both of these possible conjugate acids, and explain (resonance) why the correct one is more stable. Calculate the pKa of this conjugate acid.
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Textbook Question
Consider each pair of bases, and explain which one is more basic. Draw their conjugate acids, and show which one is a stronger acid.
(a)
(b)
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1
rank
Textbook Question
Choose the more basic member of each pair of isomers, and show why the base you chose is more basic.
(a)
(b)
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Textbook Question
Choose the more acidic member of each pair of isomers, and show why the acid you chose is more acidic.
(d)
(e)
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Textbook Question
Choose the more acidic member of each pair of isomers, and show why the acid you chose is more acidic.
(f)
(g)
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