Textbook Question
Show how you would accomplish the following synthetic transformations. Show all intermediates.
b. 2,2-dibromobutane → but-2-yne
1
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Ch.9 - Alkynes
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 9, Problem 33g,h,i
Predict the products of reaction of pent-1-yne with the following reagents.
g. cold, dilute KMnO4
h. warm, concd. KMnO4, NaOH
i. Na, liquid ammonia
Verified step by step guidance1
Step 1: Understand the structure of pent-1-yne. It is a terminal alkyne with the molecular formula C5H8, where the triple bond is located between the first and second carbon atoms.
Step 2: For reaction (g) with cold, dilute KMnO4, recognize that this reagent performs mild oxidation. It adds hydroxyl groups (-OH) across the triple bond, resulting in a diol. Specifically, the triple bond will be converted into a cis-diol (two hydroxyl groups on adjacent carbons).
Step 3: For reaction (h) with warm, concentrated KMnO4 in the presence of NaOH, understand that this is a strong oxidative cleavage reaction. The triple bond will be completely broken, and the alkyne will be oxidized to carboxylic acids. Since pent-1-yne is a terminal alkyne, one product will be a carboxylic acid (R-COOH), and the other will be carbon dioxide (CO2).
Step 4: For reaction (i) with sodium (Na) in liquid ammonia, recognize that this is a reduction reaction. Sodium in liquid ammonia reduces alkynes to trans-alkenes. The triple bond in pent-1-yne will be reduced to a trans-alkene, specifically trans-pent-2-ene.
Step 5: Summarize the products for each reaction: (g) cis-diol from mild oxidation, (h) carboxylic acid and CO2 from oxidative cleavage, and (i) trans-alkene from reduction. Ensure you understand the role of each reagent and the type of reaction it facilitates.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alkyne Reactivity
Alkynes, such as pent-1-yne, are hydrocarbons with a carbon-carbon triple bond. Their reactivity is influenced by the presence of this triple bond, which can undergo various reactions, including addition and oxidation. Understanding how alkynes react with different reagents is crucial for predicting the products of these reactions.
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Alkyne Hydration
Oxidation Reactions
Oxidation reactions involve the addition of oxygen or the removal of hydrogen from a molecule. In the context of alkynes, reagents like cold, dilute KMnO4 (Bayer's reagent) can lead to syn-dihydroxylation, while warm, concentrated KMnO4 can oxidatively cleave the triple bond, resulting in carboxylic acids. Recognizing the type of oxidation and its conditions is essential for predicting the products.
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Reduction Reactions
Reduction reactions involve the gain of electrons or hydrogen, often resulting in the conversion of a triple bond to a double or single bond. The reaction of pent-1-yne with sodium in liquid ammonia is a classic example of a reduction that can yield a trans-alkene. Understanding the mechanisms of reduction helps in predicting the structural outcomes of such reactions.
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Related Practice
Textbook Question
Muscalure, the sex attractant of the common housefly, is cis-tricos-9-ene. Most syntheses of alkenes give the more stable trans isomer as the major product. Devise a synthesis of muscalure from acetylene and other compounds of your choice. Your synthesis must give specifically the cis isomer of muscalure.
Textbook Question
Show how you would accomplish the following synthetic transformations. Show all intermediates.
a. 2,2-dibromobutane → but-1-yne
1
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Textbook Question
Predict the products of reaction of pent-1-yne with the following reagents.
d. H2, Pd/BaSO4, quinoline
e. 1 equivalent of Br2
f. 2 equivalents of Br2
5
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Textbook Question
Predict the products of reaction of pent-1-yne with the following reagents.
a. 1 equivalent of HCl
b. 2 equivalents of HCl
c. excess H2, Ni
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Textbook Question
Predict the products of reaction of pent-1-yne with the following reagents.
j. NaNH2
k. H2SO4/HgSO4, H2O
l. Sia2BH, then H2O2, –OH
4
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