Textbook Question
Which reacts faster in an SN1 reaction?
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Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides
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. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 40
Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 40Chapter 10, Problem 40
You were told in [SECTION 7.11] that is best to use a methyl halide or a primary alkyl halide for the reaction of an acetylide ion with an alkyl halide. Explain why this is so.
Verified step by step guidance1
The reaction between an acetylide ion (a strong nucleophile) and an alkyl halide proceeds via an SN2 (bimolecular nucleophilic substitution) mechanism. In an SN2 reaction, the nucleophile attacks the electrophilic carbon of the alkyl halide from the opposite side of the leaving group, leading to a single-step, concerted reaction.
For an SN2 reaction to occur efficiently, steric hindrance around the electrophilic carbon must be minimal. Methyl halides and primary alkyl halides have less steric hindrance compared to secondary or tertiary alkyl halides, making them more reactive in SN2 reactions.
If a secondary or tertiary alkyl halide is used, the increased steric hindrance around the electrophilic carbon slows down or prevents the SN2 reaction. Additionally, tertiary alkyl halides are more likely to undergo elimination (E2) reactions instead of substitution.
The acetylide ion is a strong base as well as a strong nucleophile. When reacting with secondary or tertiary alkyl halides, the likelihood of elimination (E2) increases due to the steric hindrance, which makes substitution less favorable.
Therefore, using a methyl halide or a primary alkyl halide ensures that the reaction proceeds efficiently via the SN2 mechanism, avoiding complications such as steric hindrance or competing elimination reactions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acetylide Ion Reactivity
Acetylide ions are strong nucleophiles due to the high electron density on the carbon atom. This makes them highly reactive towards electrophiles, such as alkyl halides. Understanding the nucleophilicity of acetylide ions is crucial for predicting the outcome of reactions involving these species.
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Metal Ion Catalysis Example 1
SN2 Mechanism
The reaction between acetylide ions and alkyl halides typically follows an SN2 mechanism, where the nucleophile attacks the electrophile from the opposite side of the leaving group. This mechanism is favored with primary alkyl halides because they provide less steric hindrance, allowing for a more efficient reaction.
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08:33Drawing the SN2 Mechanism
Steric Hindrance
Steric hindrance refers to the crowding around a reactive site that can impede the approach of a nucleophile. Methyl and primary alkyl halides have minimal steric hindrance, making them more suitable for reactions with acetylide ions. In contrast, secondary and tertiary halides are less reactive due to increased steric hindrance, which can slow down or prevent the reaction.
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02:53Understanding steric effects.
Related Practice
Textbook Question
a. Explain why 1-bromo-2,2-dimethylpropane has difficulty undergoing both SN2 and SN1 reactions.
b. Can it undergo E2 and E1 reactions?
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Textbook Question
Which reacts faster in an SN2 reaction?
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Textbook Question
Explain why only a substitution product and no elimination product is obtained when the following compound reacts with sodium methoxide:
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Textbook Question
Which reacts faster in an E1 reaction?
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Textbook Question
How does the ratio of substitution product to elimination product formed from the reaction of propyl bromide with CH3O− in methanol change if the nucleophile is changed to CH3S−?
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