Textbook Question
Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(b) Li+ vs. Na+
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Ch. 20 - Enolates: Carbonyl Addition and Substitution
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 19, Problem 18a
Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(a) Al3+ vs. B3+
Verified step by step guidance1
Step 1: Recall the definition of a Lewis acid. A Lewis acid is a species that can accept a pair of electrons. The strength of a Lewis acid depends on factors such as charge density, electronegativity, and the size of the ion.
Step 2: Compare the charges of Al³⁺ and B³⁺. Both ions have a +3 charge, which means they have the same formal charge. However, the size of the ion and its charge density will play a significant role in determining which is the harder Lewis acid.
Step 3: Consider the size of the ions. Aluminum (Al) is in Period 3 of the periodic table, while boron (B) is in Period 2. This means that Al³⁺ is larger in size compared to B³⁺. A smaller ion like B³⁺ will have a higher charge density because the +3 charge is concentrated over a smaller volume.
Step 4: Analyze the charge density. Since B³⁺ has a smaller ionic radius and a higher charge density compared to Al³⁺, it will have a stronger ability to attract electron pairs, making it a harder Lewis acid.
Step 5: Conclude that B³⁺ is the harder Lewis acid due to its smaller size and higher charge density, which increases its ability to accept electron pairs. This conclusion is based on fundamental principles of charge density and periodic trends, not just referencing a table.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Lewis Acids and Bases
Lewis acids are defined as electron pair acceptors, while Lewis bases are electron pair donors. This concept is fundamental in understanding acid-base reactions in organic chemistry, as it expands the traditional Brønsted-Lowry definitions. The strength of a Lewis acid is influenced by its ability to stabilize the resulting complex after accepting an electron pair.
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02:49
The Lewis definition of acids and bases.
Charge Density
Charge density refers to the distribution of electric charge over a given volume. In the context of Lewis acids, a higher charge density typically indicates a stronger acid, as it can attract electron pairs more effectively. For cations like Al³⁺ and B³⁺, the charge density is influenced by their ionic radii and the magnitude of their positive charge.
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01:34Calculating formal and net charge.
Stability of the Conjugate Base
The stability of the conjugate base formed after a Lewis acid accepts an electron pair is crucial in determining the strength of the acid. A more stable conjugate base will favor the forward reaction, making the original species a stronger Lewis acid. Factors such as electronegativity and resonance can significantly affect the stability of the conjugate base.
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04:31Stability of Conjugated Intermediates
Related Practice
Textbook Question
LDA can be used to form enolates on esters and nitriles. Predict the product of these alkylation reactions.
(a)
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Textbook Question
Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(c) Mg2+ vs. Na+
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Textbook Question
Specify which in each pair is the harder Lewis base. Justify your choice beyond just looking at Table 20.2.
(c) I- vs. F-
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Textbook Question
Which of the following SN2 and E2 reactions, respectively, is faster? Justify your choice.
(b)
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Textbook Question
Specify which in each pair is the harder Lewis base. Justify your choice beyond just looking at Table 20.2.
(b)