Textbook Question
Predict the major products of the following reactions.
(c) 2-methylpent-2-ene + BH3⋅THF
(d) the product from part (c) + H2O2/OH−
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Ch.8 - Reactions of Alkenes
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 8, Problem 9c
Show how you would accomplish the following synthetic conversions.
c. 3-methylpent-1-ene → 3-methylpentan-2-ol
Explain why acid-catalyzed hydration would be a poor choice for the reaction in (c).
Verified step by step guidance1
Step 1: Analyze the starting material and the target product. The starting material is 3-methylpent-1-ene, an alkene, and the target product is 3-methylpentan-2-ol, an alcohol. This indicates that the reaction involves the addition of an -OH group to the alkene, specifically at the second carbon.
Step 2: Recognize that acid-catalyzed hydration of alkenes typically follows Markovnikov's rule, where the -OH group adds to the more substituted carbon. However, in this case, acid-catalyzed hydration would lead to the formation of 3-methylpentan-3-ol (not 3-methylpentan-2-ol) due to carbocation rearrangement. This makes acid-catalyzed hydration a poor choice.
Step 3: To achieve the desired product, use hydroboration-oxidation as the reaction mechanism. This method involves two steps: (1) hydroboration, where BH₃ or a borane derivative adds to the alkene in an anti-Markovnikov fashion, and (2) oxidation, where the boron atom is replaced by an -OH group using hydrogen peroxide (H₂O₂) in a basic medium (NaOH).
Step 4: Write the reaction sequence. In the first step, treat 3-methylpent-1-ene with BH₃·THF (borane in tetrahydrofuran) to form the organoborane intermediate. In the second step, oxidize the intermediate with H₂O₂/NaOH to yield 3-methylpentan-2-ol.
Step 5: Summarize why hydroboration-oxidation is the preferred method. It avoids carbocation rearrangement and ensures anti-Markovnikov addition, leading to the formation of the desired product, 3-methylpentan-2-ol, with high regioselectivity.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydration Reactions
Hydration reactions involve the addition of water to an alkene, resulting in the formation of alcohols. In acid-catalyzed hydration, an acid protonates the alkene, creating a more stable carbocation intermediate that can then react with water. This process is typically regioselective, favoring the formation of the more stable alcohol, but can lead to rearrangements that complicate the desired product formation.
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Alkyne Hydration
Carbocation Stability
Carbocation stability is crucial in determining the outcome of reactions involving carbocations. Tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects. In the case of 3-methylpent-1-ene, the formation of a secondary carbocation during acid-catalyzed hydration may lead to rearrangements, resulting in undesired products rather than the target 3-methylpentan-2-ol.
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Markovnikov's Rule
Markovnikov's Rule states that in the addition of HX to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms, leading to the more stable carbocation. In the context of the conversion from 3-methylpent-1-ene to 3-methylpentan-2-ol, applying this rule could lead to the formation of a different alcohol than intended, making acid-catalyzed hydration a poor choice for achieving the desired product.
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Related Practice
Textbook Question
Predict the major products of the following reactions.
a. propene + BH3⋅THF
b. the product from part (a) + H2O2/OH−
2220
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Textbook Question
Show how you would accomplish the following synthetic conversions.
a. but-1-ene → butan-1-ol
1628
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Textbook Question
Predict the major products of the following reactions.
c. 4−chlorocycloheptene + Hg(OAc)2 in CH3OH
d. the product from part (c), treated with NaBH4
1139
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Textbook Question
Show how you would accomplish the following synthetic conversions.
a. but-1-ene → 2-methoxybutane
b. 1-iodo-2-methylcyclopentane → 1-methylcyclopentanol
1169
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Textbook Question
Predict the major products of the following reactions.
a. 1-methylcyclohexene+ aqueous Hg(OAc)2
b. the product from part (a), treated with NaBH4
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