Textbook Question
Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(a) Al3+ vs. B3+
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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 18b
Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(b) Li+ vs. Na+
Verified step by step guidance1
Step 1: Recall the definition of a Lewis acid. A Lewis acid is a species that can accept an electron pair. Hard Lewis acids are typically small, highly charged, and have low polarizability.
Step 2: Compare the two ions, Li+ and Na+. Both are alkali metal cations, but they differ in size and charge density. Li+ is smaller in size compared to Na+, which means it has a higher charge density.
Step 3: Higher charge density makes Li+ a stronger Lewis acid because it can attract electron pairs more effectively due to its concentrated positive charge.
Step 4: Consider polarizability. Li+ is less polarizable than Na+ because of its smaller size and tighter electron cloud. This characteristic aligns with the properties of hard acids, making Li+ harder than Na+.
Step 5: Justify the choice using the table provided. Both Li+ and Na+ are listed under hard acids, but Li+ is harder due to its smaller ionic radius and higher charge density, which are key factors in determining the hardness of a Lewis acid.
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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 species that can accept an electron pair, while Lewis bases are those that can donate an electron pair. This concept is fundamental in understanding acid-base reactions in organic chemistry, as it expands the definition beyond protons (Brønsted acids) to include a wider range of chemical interactions. The strength of a Lewis acid is often determined by its ability to stabilize the negative charge of the electron pair it accepts.
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The Lewis definition of acids and bases.
Hard and Soft Acids and Bases (HSAB) Theory
The HSAB theory categorizes acids and bases as 'hard' or 'soft' based on their charge density and polarizability. Hard acids, like Li<sup>+</sup>, have small size and high charge density, making them less polarizable and more stable in reactions with hard bases. In contrast, soft acids, such as Na<sup>+</sup>, are larger and more polarizable, favoring interactions with soft bases. This classification helps predict the stability and reactivity of acid-base pairs.
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02:49The Lewis definition of acids and bases.
Comparative Strength of Lewis Acids
To determine which Lewis acid is stronger between two candidates, one must consider factors such as charge density, size, and the ability to stabilize the resulting complex. In the case of Li<sup>+</sup> versus Na<sup>+</sup>, Li<sup>+</sup> is a harder acid due to its smaller ionic radius and higher charge density, making it more effective at accepting electron pairs compared to the larger, softer Na<sup>+</sup>. This comparative analysis is crucial for understanding their reactivity in various chemical environments.
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Related Practice
Textbook Question
Rank the reactivity of the following carbonyls with nucleophiles, from least reactive to most reactive.
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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.
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Specify which in each pair is the harder Lewis base. Justify your choice beyond just looking at Table 20.2.
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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.
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