Textbook Question
Why does cis-2-butene have a higher boiling point than trans-2-butene?
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Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 7 - The Reactions of Alkynes • An Introduction to Multistep SynthesisProblem 13a
Bruice 8th EditionCh. 7 - The Reactions of Alkynes • An Introduction to Multistep SynthesisProblem 13aChapter 8, Problem 13a
Drawing on what you know about the stereochemistry of alkene addition reactions,
a. write the mechanism for the reaction of 2-butyne with one equivalent of Br2.
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Identify the starting material, 2-butyne, which is a symmetrical alkyne with the structure CH≡C-CH3. Recognize that the reaction involves the addition of one equivalent of bromine (Br2) to the triple bond.
Understand the mechanism: The reaction proceeds via an electrophilic addition mechanism. The π-electrons of the triple bond attack the Br2 molecule, causing polarization of the Br-Br bond and forming a cyclic bromonium ion intermediate.
Draw the cyclic bromonium ion intermediate: The triple bond is partially broken, and one bromine atom is attached to one of the carbons of the former triple bond, while the other bromine atom forms a three-membered ring with the adjacent carbon.
Explain the stereochemistry: The bromonium ion intermediate is attacked by the second bromine ion (Br⁻) in an anti-addition manner. This means the two bromine atoms will add to opposite sides of the molecule, resulting in a trans-configuration of the product.
Draw the final product: The addition of one equivalent of Br2 to 2-butyne results in a trans-dibromoalkene, specifically trans-2,3-dibromo-2-butene. Ensure the stereochemistry is clearly shown in the structure.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Stereochemistry
Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the context of alkene addition reactions, it is crucial to understand how the orientation of substituents around the double bond can lead to different stereoisomers, such as cis and trans forms, which can have distinct physical and chemical properties.
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Alkene Addition Reactions
Alkene addition reactions involve the addition of reagents across the carbon-carbon double bond, converting the alkene into a saturated compound. The mechanism typically involves the formation of a cyclic intermediate (bromonium ion in the case of Br2), which influences the stereochemical outcome of the reaction, leading to either syn or anti addition of the halogen atoms.
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Mechanism of Bromination
The mechanism of bromination of alkenes involves the electrophilic attack of bromine on the double bond, forming a bromonium ion intermediate. This intermediate is then attacked by a bromide ion, leading to the formation of vicinal dibromides. Understanding this mechanism is essential for predicting the stereochemical outcome of the reaction, particularly whether the addition occurs in a syn or anti manner.
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00:54Mechanism of Allylic Bromination.
Related Practice
Textbook Question
Drawing on what you know about the stereochemistry of alkene addition reactions,
b. predict the configuration of the product of the reaction.
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Textbook Question
What orbitals are used to form the carbon–carbon s bond between the highlighted carbons?
g.
h.
i.
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Textbook Question
What ketones are formed from the acid-catalyzed hydration of 3-heptyne?
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Textbook Question
In Table 7.2, what is the smallest alkane, the smallest terminal alkene, and the smallest terminal alkyne that are liquids at room temperature, which is generally taken to be 20 °C to 25 °C?
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Textbook Question
Which alkyne should be used for the synthesis of each of the following ketones?
a.
b.
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