Textbook Question
Benzyl ethers make excellent protecting groups according to the general scheme shown here.
(a) How would you protect the 1° alcohol as a benzyl ether in the first step?
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Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination
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
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Mullins 1st EditionCh. 13 - Alcohols, Ethers and Related Compounds: Substitution and EliminationProblem 117b
Mullins 1st EditionCh. 13 - Alcohols, Ethers and Related Compounds: Substitution and EliminationProblem 117bChapter 12, Problem 117b
The acid-catalyzed dehydration we learned in this chapter is reversible, as shown below.
(b) Without looking back, how do you know this mechanism is correct?
Verified step by step guidance1
Step 1: Recognize that the reaction shown is an acid-catalyzed hydration-dehydration equilibrium. The presence of H₂SO₄ (sulfuric acid) indicates acid catalysis, which facilitates both the addition of water to the alkene and the reverse dehydration reaction.
Step 2: Understand the mechanism of acid-catalyzed hydration. The alkene undergoes protonation by H⁺ from H₂SO₄, forming a carbocation intermediate. This intermediate is stabilized and then attacked by water (H₂O), leading to the formation of the alcohol product.
Step 3: Recall that the reverse reaction (dehydration) is also acid-catalyzed. The alcohol can lose a proton to form a carbocation, followed by elimination of water to regenerate the alkene. This reversibility is a hallmark of acid-catalyzed hydration-dehydration reactions.
Step 4: Verify the correctness of the mechanism by considering Markovnikov's rule. In the hydration step, the proton adds to the less substituted carbon of the double bond, forming the more stable carbocation intermediate, which leads to the correct alcohol product.
Step 5: Confirm that the reaction is consistent with principles of equilibrium. The reaction can proceed in either direction depending on the conditions (e.g., excess water favors hydration, while removal of water favors dehydration). This reversibility ensures the mechanism is correct.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Catalyzed Dehydration
Acid-catalyzed dehydration is a chemical reaction where an alcohol is converted into an alkene through the removal of a water molecule, facilitated by an acid. This process typically involves protonation of the alcohol, leading to the formation of a better leaving group, and subsequent elimination of water. Understanding this mechanism is crucial as it highlights the role of acids in promoting the reaction and the reversibility of the process.
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General features of acid-catalyzed dehydration.
Reversibility of Reactions
Reversibility in chemical reactions refers to the ability of a reaction to proceed in both the forward and reverse directions. In the context of acid-catalyzed dehydration, this means that the formation of the alkene can be reversed by the addition of water, regenerating the alcohol. Recognizing this characteristic is essential for predicting the behavior of the reaction under different conditions and understanding equilibrium.
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Mechanism of Reaction
The mechanism of a reaction describes the step-by-step sequence of elementary reactions that lead to the overall transformation of reactants into products. In acid-catalyzed dehydration, the mechanism involves protonation, formation of a carbocation, and elimination of water. Knowing the mechanism is vital for validating the correctness of the reaction pathway and for predicting the products formed under various conditions.
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Related Practice
Textbook Question
Assessment 8.74 revealed that oxymercuration could be used to make cyclic esters. Suggest a likely mechanism for this transformation.
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Textbook Question
Suggest a mechanism for the following substitution reaction.
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Textbook Question
The acid-catalyzed dehydration we learned in this chapter is reversible, as shown below.
(c) Which side of the reaction would be favored by running the reaction at low temperatures?
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Textbook Question
The acid-catalyzed dehydration we learned in this chapter is reversible, as shown below.
(a) Propose a mechanism for the formation of an alcohol from an alkene.
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Textbook Question
The acid-catalyzed dehydration we learned in this chapter is reversible, as shown below.
(d) How might you shift the equilibrium to the right?
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