Textbook Question
What is the major elimination product obtained from the reaction of each of the following alkyl halides with hydroxide ion?
c.
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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 19
Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 19Chapter 10, Problem 19
Rank the following alkyl halides from most reactive to least reactive in an SN1 reaction:
2-bromo-2-methylpentane, 2-chloro-2-methylpentane, 3-chloropentane, and 2-iodo-2-methylpentane.
Verified step by step guidance1
Step 1: Recall the key factors that influence the reactivity of alkyl halides in an SN1 reaction. The SN1 mechanism involves the formation of a carbocation intermediate, so the stability of the carbocation is a critical factor. Additionally, the leaving group ability plays a significant role in determining the reaction rate.
Step 2: Analyze the carbocation stability for each alkyl halide. The carbocation formed from 2-bromo-2-methylpentane, 2-chloro-2-methylpentane, and 2-iodo-2-methylpentane will be tertiary (due to the carbon attached to three alkyl groups), which is more stable than the secondary carbocation formed from 3-chloropentane. Therefore, the tertiary alkyl halides will generally react faster in an SN1 reaction than the secondary alkyl halide.
Step 3: Evaluate the leaving group ability of each halogen. The leaving group ability increases in the order: Cl⁻ < Br⁻ < I⁻. This means that 2-iodo-2-methylpentane will have the best leaving group, followed by 2-bromo-2-methylpentane, and then 2-chloro-2-methylpentane. 3-chloropentane, with a chlorine leaving group, will have the weakest leaving group among the options.
Step 4: Combine the effects of carbocation stability and leaving group ability. Since 2-iodo-2-methylpentane has both a tertiary carbocation and the best leaving group, it will be the most reactive. 2-bromo-2-methylpentane, with a tertiary carbocation and a good leaving group, will be the next most reactive. 2-chloro-2-methylpentane, with a tertiary carbocation but a weaker leaving group, will follow. Finally, 3-chloropentane, with a secondary carbocation and a weak leaving group, will be the least reactive.
Step 5: Rank the alkyl halides in order of reactivity for an SN1 reaction: 2-iodo-2-methylpentane > 2-bromo-2-methylpentane > 2-chloro-2-methylpentane > 3-chloropentane.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
SN1 Reaction Mechanism
The SN1 (Substitution Nucleophilic Unimolecular) reaction mechanism involves two main steps: the formation of a carbocation intermediate and the subsequent nucleophilic attack. The rate of the reaction depends solely on the concentration of the alkyl halide, making it unimolecular. This mechanism is favored in tertiary and some secondary alkyl halides due to their ability to stabilize the carbocation formed during the reaction.
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Drawing the SN1 Mechanism
Carbocation Stability
Carbocation stability is a crucial factor in determining the reactivity of alkyl halides in SN1 reactions. Tertiary carbocations are more stable than secondary, which are more stable than primary due to hyperconjugation and inductive effects. The more stable the carbocation, the faster the reaction will proceed, as the formation of the carbocation is the rate-determining step in the SN1 mechanism.
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05:58Determining Carbocation Stability
Leaving Group Ability
The ability of a leaving group to depart from the substrate is essential in determining the reactivity of alkyl halides in SN1 reactions. Iodine is a better leaving group than bromine, which is better than chlorine, due to the bond strength and the stability of the leaving group after departure. Thus, alkyl halides with better leaving groups will generally react more quickly in SN1 reactions.
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03:06How to use the factors affecting acidity to predict leaving group ability.
Related Practice
Textbook Question
Draw the stereoisomers that are formed from the following SN1 reactions:
a. 3-bromo-3-methylpentane and methanol
b. 3-chloro-3-methylhexane and methanol
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Textbook Question
Which of the following reactions take place more rapidly when the concentration of the nucleophile is increased?
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Textbook Question
Explain why a much better yield of primary amine is obtained from the reaction of an alkyl halide with azide ion (-N3), followed by catalytic hydrogenation. (Hint: An alkyl azide is not nucleophilic.)
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Textbook Question
Explain why the reaction of an alkyl halide with ammonia gives a low yield of primary amine.
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Textbook Question
What is the major elimination product obtained from the reaction of each of the following alkyl halides with hydroxide ion?
a.
b.
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