Textbook Question
The nitro group directs electrophilic aromatic substitution to the meta position. After reduction by hydrogenation, to which carbon(s) does it direct?
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Ch. 25 - Amines: Structure, Reactions, and Synthesis
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 24, Problem 46b
Given the pKb, calculate the pKa of the conjugate acid.
(b) 
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Understand the relationship between pKa and pKb. The pKa of a conjugate acid and the pKb of its conjugate base are related by the equation: (at 25°C). This is derived from the ionization constant of water, Kw, where .
Rearrange the equation to solve for pKa: .
Substitute the given value of pKb into the equation. For example, if pKb = 4.75, substitute it into the equation: .
Perform the subtraction to determine the pKa value. This step involves simple arithmetic, but ensure you understand the concept of how pKa and pKb are inversely related.
Interpret the result. A lower pKa value indicates a stronger conjugate acid, while a higher pKa value indicates a weaker conjugate acid. This relationship is important in understanding acid-base chemistry.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
pKb and pKa Definitions
pKb is the negative logarithm of the base dissociation constant (Kb) of a weak base, indicating its strength. Conversely, pKa is the negative logarithm of the acid dissociation constant (Ka) of a weak acid. The relationship between pKa and pKb is crucial for understanding acid-base equilibria, as they are related through the equation: pKa + pKb = 14 at 25°C.
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Conjugate Acid-Base Pairs
In acid-base chemistry, a conjugate acid is formed when a base accepts a proton (H+). Each acid has a corresponding conjugate base, which is what remains after the acid donates a proton. Understanding these pairs is essential for calculating pKa from pKb, as it allows for the identification of the acid's strength based on its conjugate base's properties.
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Calculating pKa from pKb
To calculate the pKa of a conjugate acid from its pKb, one can use the formula: pKa = 14 - pKb. This equation reflects the inverse relationship between the strength of a base and its conjugate acid. By knowing the pKb value, one can easily determine the pKa, which is vital for predicting the behavior of acids and bases in various chemical reactions.
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Related Practice
Textbook Question
Despite the amino group being an ortho/para director, nitration of aniline gives the meta isomer predominantly. Explain this result.
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Textbook Question
Calculate the equilibrium constant for each of the acid–base reactions shown.
b.
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Textbook Question
Following a LiAlH₄ reduction, an IR spectrum suggested that the product was a mixture of the starting amide and the desired amine.
(b) Once separated, how could you distinguish between the amide and the amine using IR spectroscopy?
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Textbook Question
Given the starting reactant, suggest a method for synthesizing the amine on the right.
(b)
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Textbook Question
Given the pKb, calculate the pKa of the conjugate acid.
(c)
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