Textbook Question
Explain why the acid-catalyzed condensation is a poor method for the synthesis of an unsymmetrical ether such as ethyl methyl ether, CH3CH2-O-CH3.
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Ch.11 - Reactions of Alcohols
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 11, Problem 26a
Propose a mechanism for each reaction.
(a) 
Verified step by step guidance1
Step 1: Recognize the reaction type. This is an acid-catalyzed dehydration reaction where an alcohol is converted into an alkene using concentrated sulfuric acid (H₂SO₄) and heat.
Step 2: Protonation of the alcohol group. The hydroxyl group (-OH) on the cyclopentanol molecule is protonated by H₂SO₄, forming a good leaving group (water). The protonation step increases the electrophilicity of the carbon attached to the hydroxyl group.
Step 3: Formation of the carbocation intermediate. The protonated hydroxyl group leaves as water, generating a carbocation intermediate on the cyclopentane ring. This step is crucial for the subsequent rearrangement or elimination.
Step 4: Elimination of a proton to form the double bond. A base (often HSO₄⁻ or water) abstracts a proton from a β-carbon adjacent to the carbocation, leading to the formation of a double bond (alkene) in the cyclopentane ring.
Step 5: Verify the product. The final product is cyclopentene, an alkene formed by the elimination of water from cyclopentanol. The reaction follows Zaitsev's rule, favoring the most substituted alkene.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reaction Mechanism
A reaction mechanism is a step-by-step description of how reactants transform into products in a chemical reaction. It outlines the sequence of elementary steps, including bond breaking and forming, and the intermediates involved. Understanding the mechanism helps predict the outcome of reactions and the conditions required for them to occur.
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Types of Organic Reactions
Organic reactions can be classified into several types, including substitution, addition, elimination, and rearrangement reactions. Each type has distinct characteristics and mechanisms. Recognizing the type of reaction is crucial for proposing an accurate mechanism, as it influences the pathways and intermediates formed during the reaction.
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Curved Arrow Notation
Curved arrow notation is a visual representation used in organic chemistry to illustrate the movement of electrons during a reaction. Arrows indicate the direction of electron flow, showing how bonds are broken and formed. Mastery of this notation is essential for accurately depicting reaction mechanisms and understanding the underlying electron transfer processes.
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Related Practice
Textbook Question
Some alcohols undergo rearrangement or other unwanted side reactions when they dehydrate in acid. Alcohols may be dehydrated under mildly basic conditions using phosphorus oxy-chloride (POCl3) in pyridine. The alcohol reacts with phosphorus oxychloride much like it reacts with tosyl chloride (Section 11-5), displacing a chloride ion from phosphorus to give an alkyl dichlorophosphate ester. The dichlorophosphate group is an outstanding leaving group. Pyridine reacts as a base with the dichlorophosphate ester to give an E2 elimination. Propose a mechanism for the dehydration of cyclohexanol by POCl3 in pyridine.
Textbook Question
Contrast the mechanisms of the two preceding reactions, the dehydration and condensation of ethanol.
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Textbook Question
Propose a mechanism for each reaction.
(a)
(b)
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Textbook Question
When the following substituted cycloheptanol undergoes dehydration, one of the minor products has undergone a ring contraction. Propose a mechanism to show how this ring contraction occurs.
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Textbook Question
Propose a mechanism for each reaction.
(c)
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