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 18c
Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(c) Mg2+ 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 a pair of electrons. Hard Lewis acids are typically small, highly charged, and have low polarizability.
Step 2: Analyze the chemical properties of Mg2+ and Na+. Mg2+ is a divalent cation (charge of +2), while Na+ is a monovalent cation (charge of +1). Higher charge density generally makes a species a harder Lewis acid.
Step 3: Consider the size of the ions. Mg2+ is smaller in size compared to Na+, which increases its charge density and makes it a harder Lewis acid.
Step 4: Refer to the table provided. Mg2+ is explicitly listed under 'Hard acids,' while Na+ is also listed under 'Hard acids.' However, Mg2+ is harder due to its higher charge density and smaller ionic radius.
Step 5: Justify the choice beyond the table. The hardness of Mg2+ compared to Na+ can be explained by its stronger electrostatic attraction to electron pairs due to its higher charge and smaller size, which aligns with the principles of hard and soft acid-base theory.
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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 Mg²⁺, have high charge density and prefer to interact with hard bases, while soft acids, like Na⁺, have lower charge density and interact better with soft bases. This classification helps predict the stability of complexes and the outcome of chemical reactions, making it essential for comparing the strength of Lewis acids.
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Comparative Strength of Lewis Acids
When comparing Lewis acids, factors such as charge, size, and electronegativity play crucial roles in determining their strength. For instance, Mg²⁺ is a harder Lewis acid than Na⁺ due to its higher charge and smaller ionic radius, which leads to stronger interactions with electron pairs. Understanding these differences is vital for predicting reactivity and selectivity in organic reactions, especially when analyzing pairs of acids.
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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
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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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 base. Justify your choice beyond just looking at Table 20.2.
(c) I- vs. F-
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Textbook Question
Identify the enolate(s) that would form on treatment of each of the following carbonyls with base. [When there are two possibilities, draw both.]
(a)
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