Textbook Question
Does methanol behave as an acid or a base when it reacts with methylamine?
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Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry
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. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 12c,d
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 12c,dChapter 3, Problem 12c,d
Estimate the pKa values of the following compounds:
c. CH3CH2COOH
d. CH3CH2CH2N+H3
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Identify the functional group in each compound. For CH3CH2COOH, the functional group is a carboxylic acid (-COOH). For CH3CH2CH2N+H3, the functional group is a protonated amine (-N+H3).
Recall the typical pKa ranges for these functional groups. Carboxylic acids generally have pKa values around 4-5, while protonated amines typically have pKa values around 9-11.
Consider the structure of CH3CH2COOH. The ethyl group (CH3CH2-) is an electron-donating group, but it has minimal effect on the acidity of the carboxylic acid. Therefore, the pKa will remain close to the typical range for carboxylic acids.
For CH3CH2CH2N+H3, the propyl group (CH3CH2CH2-) is also an electron-donating group, but it does not significantly affect the pKa of the protonated amine. The pKa will remain close to the typical range for protonated amines.
To estimate the pKa values, use the typical ranges for the functional groups as a guide. CH3CH2COOH will have a pKa around 4-5, and CH3CH2CH2N+H3 will have a pKa around 9-11. These are approximate values based on the functional groups and their typical behavior in aqueous solution.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
pKa and Acid Strength
pKa is a quantitative measure of the strength of an acid in solution. It is the negative logarithm of the acid dissociation constant (Ka), which indicates how easily an acid donates a proton (H+). Lower pKa values correspond to stronger acids, as they dissociate more completely in solution.
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Identifying pKa values
Carboxylic Acids
Carboxylic acids, such as CH3CH2COOH (propanoic acid), contain a carboxyl group (-COOH) that is responsible for their acidic properties. The presence of electronegative oxygen atoms stabilizes the negative charge on the conjugate base after deprotonation, which contributes to the acid's strength and its pKa value.
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Ammonium Ions
Ammonium ions, like CH3CH2CH2N+H3, are positively charged species formed when ammonia (NH3) accepts a proton. The pKa of ammonium ions reflects their ability to donate a proton to revert to ammonia. Understanding the pKa of ammonium ions is crucial for predicting their behavior in acid-base reactions.
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Related Practice
Textbook Question
For each of the acid–base reactions in [Section 2.3], compare the pKa values of the acids on either side of the equilibrium arrows to prove that the equilibrium lies in the direction indicated.
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Textbook Question
Butyric acid, the compound responsible for the unpleasant odor and taste of sour milk, has a pKa value of 4.82. What is its Ka value? Is it a stronger acid or a weaker acid than vitamin C?
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Textbook Question
Draw the conjugate acid of each of the following:
a. CH3CH2OH
b. CH3CH2O−
c.
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Textbook Question
Antacids are compounds that neutralize stomach acid. Write the equations that show how Milk of Magnesia, Alka-Seltzer, and Tums remove excess acid.
a. Milk of Magnesia: Mg(OH)2
b. Alka-Seltzer: KHCO3 and NaHCO3
c. Tums: CaCO3
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Textbook Question
a. Which is a stronger base: CH3COO− or HCOO−? (The pKa of CH3COOH is 4.8; the pKa of HCOOH is 3.8.)
b. Which is a stronger base: HO− or -NH2? (The pKa of H2O is 15.7; the pKa of NH3 is 36.)
c. Which is a stronger base: H2O or CH3OH? (The pKa of H3O+ is −1.7; the pKa of CH3O+H2 is −2.5.)
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