Textbook Question
Propose a mechanism for the bromination of ethylbenzene shown below.
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Ch. 17 - Reactions of Aromatic Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 17, Problem 37
Propose a mechanism for the reaction of benzyl bromide with ethanol to give benzyl ethyl ether.
Verified step by step guidance1
Step 1: Identify the reaction type. This is a nucleophilic substitution reaction where benzyl bromide reacts with ethanol under heat to form benzyl ethyl ether. The bromine atom is replaced by the ethoxy group (-OCH2CH3).
Step 2: Analyze the structure of benzyl bromide. Benzyl bromide contains a benzyl group (C6H5CH2-) attached to a bromine atom. The benzyl group stabilizes the carbocation intermediate formed during the reaction.
Step 3: Ethanol acts as the nucleophile. The oxygen atom in ethanol has lone pairs of electrons, making it nucleophilic and capable of attacking the electrophilic carbon in benzyl bromide.
Step 4: Mechanism initiation. The reaction begins with the cleavage of the C-Br bond in benzyl bromide, forming a benzyl carbocation (C6H5CH2+). This step is facilitated by the heat provided in the reaction conditions.
Step 5: Nucleophilic attack. The lone pair of electrons on the oxygen atom of ethanol attacks the benzyl carbocation, forming a new C-O bond. This results in the formation of benzyl ethyl ether (C6H5CH2OCH2CH3) as the final product.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Substitution Reactions
Nucleophilic substitution reactions involve the replacement of a leaving group in a molecule by a nucleophile. In this case, the bromine atom in benzyl bromide is replaced by the ethoxide ion (from ethanol) through an SN2 mechanism, where the nucleophile attacks the electrophilic carbon, leading to the formation of the new bond.
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Nucleophiles and Electrophiles can react in Substitution Reactions.
Ethanol as a Nucleophile
Ethanol can act as a nucleophile due to the presence of the oxygen atom, which has a lone pair of electrons. When heated, ethanol can deprotonate to form the ethoxide ion (C2H5O-), which is a stronger nucleophile. This ion is crucial for attacking the benzyl carbon in benzyl bromide to form benzyl ethyl ether.
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Reaction Conditions and Mechanism
The reaction conditions, including heat, facilitate the nucleophilic substitution process. Heating increases the kinetic energy of the molecules, promoting the reaction rate. Understanding the mechanism, which involves the transition state where the nucleophile and leaving group interact, is essential for predicting the outcome of the reaction and the formation of benzyl ethyl ether.
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Related Practice
Textbook Question
Predict the major products when the following compounds are irradiated by light and treated with (1) 1 equivalent of Br2 and (2) excess Br2.
(a) isopropylbenzene
(b)
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Textbook Question
(c) Based on what you know about the relative stabilities of alkyl radicals and benzylic radicals, predict the product of addition of HBr to 1-phenylpropene in the presence of a free-radical initiator.
(d) Propose a mechanism for this reaction.
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Textbook Question
(a) Based on what you know about the relative stabilities of alkyl cations and benzylic cations, predict the product of addition of HBr to 1-phenylpropene.
(b) Propose a mechanism for this reaction.
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Textbook Question
Predict the major products of treating the following compounds with hot, concentrated potassium permanganate, followed by acidification with dilute HCl.
(a) isopropylbenzene
(b) p-xylene
(c)
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Textbook Question
Show how you would synthesize the following compounds, using the indicated starting materials.
(a) 3-phenylbutan-1-ol from styrene
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