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 117a
Mullins 1st EditionCh. 13 - Alcohols, Ethers and Related Compounds: Substitution and EliminationProblem 117aChapter 12, Problem 117a
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.
Verified step by step guidance1
Step 1: Recognize that the reaction involves the hydration of an alkene to form an alcohol. This is the reverse of the acid-catalyzed dehydration of an alcohol. The reaction proceeds via an electrophilic addition mechanism in the presence of an acid catalyst, such as H₃O⁺.
Step 2: Protonation of the alkene: The π-electrons of the alkene attack a proton (H⁺) from the acid catalyst (H₃O⁺), forming a carbocation intermediate. The stability of the carbocation depends on the substitution pattern of the alkene (tertiary > secondary > primary).
Step 3: Nucleophilic attack by water: A water molecule acts as a nucleophile and attacks the carbocation intermediate, forming an oxonium ion (R-OH₂⁺). This step is driven by the high reactivity of the carbocation.
Step 4: Deprotonation of the oxonium ion: A base (often another water molecule) removes a proton (H⁺) from the oxonium ion, resulting in the formation of the alcohol (R-OH). This step regenerates the acid catalyst (H₃O⁺), completing the catalytic cycle.
Step 5: Verify the mechanism: Ensure that the proposed mechanism is consistent with Markovnikov's rule, which states that the proton adds to the less substituted carbon of the alkene, leading to the more stable carbocation intermediate and the correct regioselectivity of the product.
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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 reaction where an alcohol is converted into an alkene through the removal of water, facilitated by an acid. This process involves protonation of the alcohol, leading to the formation of a carbocation intermediate, which can then lose a water molecule. The reaction is reversible, meaning that the alkene can also be converted back into the alcohol under appropriate conditions.
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General features of acid-catalyzed dehydration.
Mechanism of Alkene Formation
The mechanism for the formation of an alcohol from an alkene typically involves the addition of water across the double bond of the alkene, a process known as hydration. This reaction can occur via either a Markovnikov or anti-Markovnikov pathway, depending on the conditions and the presence of catalysts. The addition of water leads to the formation of a carbocation, which is then attacked by a water molecule, resulting in the formation of the alcohol.
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Carbocation Stability
Carbocation stability is a crucial concept in organic chemistry, as it influences the outcome of reactions involving carbocations. Carbocations are positively charged species that can rearrange or react to form more stable structures. The stability of a carbocation increases with the number of alkyl groups attached to the positively charged carbon, following the order: tertiary > secondary > primary. Understanding carbocation stability is essential for predicting the products of reactions involving alkenes and alcohols.
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Related Practice
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.
(b) Without looking back, how do you know this mechanism is correct?
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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.
(d) How might you shift the equilibrium to the right?
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Textbook Question
A chemist attempted the reaction below, one we introduce in Chapter 17, expecting the reaction between a strong nucleophile and a ketone in water to give an alkoxide product.
(a) Why did the reaction fail?
(b) How could the reaction conditions be changed to give a successful reaction?
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