Textbook Question
What stereoisomers are obtained from the following reactions?
c. (E)-3-methyl-2-pentene + HBr
d. cis-3-hexene + HBr
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Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions
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. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 50
Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 50Chapter 7, Problem 50
a. What is the major product obtained from the reaction of propene and Br2 plus excess Cl-?
b. Indicate the relative amounts of the stereoisomers that are obtained.
Verified step by step guidance1
Analyze the reaction: Propene (CH3-CH=CH2) reacts with Br2 in the presence of excess Cl-. This is an electrophilic addition reaction where the double bond in propene will react with Br2, forming a bromonium ion intermediate.
Step 1: The π-electrons of the double bond in propene attack one of the bromine atoms in Br2, leading to the formation of a bromonium ion intermediate. This intermediate is a three-membered ring with a positive charge on the bromine atom.
Step 2: The excess Cl- ions in the solution act as a nucleophile and attack the more substituted carbon of the bromonium ion (due to Markovnikov's rule and steric hindrance). This results in the opening of the bromonium ion ring and the formation of a vicinal (1,2-) halide product.
Step 3: Consider the stereochemistry of the product. The attack by Cl- occurs from the opposite side of the bromonium ion (anti-addition), leading to the formation of two stereoisomers: one with the bromine and chlorine atoms on opposite sides of the plane (trans) and one with them on the same side (cis).
Step 4: Indicate the relative amounts of stereoisomers. Due to the anti-addition mechanism, the trans stereoisomer is typically favored over the cis stereoisomer. The relative amounts depend on the reaction conditions, but the trans product is generally the major product.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition
Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a nucleophile, leading to the formation of a more saturated product. In the case of propene reacting with Br2, the double bond acts as a nucleophile, attacking the electrophilic bromine molecule, resulting in the formation of a bromonium ion intermediate.
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1,2 vs 1,4 Addition
Stereochemistry
Stereochemistry refers to the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. When propene reacts with Br2, the formation of stereoisomers occurs due to the different spatial orientations of the substituents around the newly formed carbon-carbon bond, leading to products that can exhibit cis/trans or E/Z configurations.
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Nucleophilic Substitution
Nucleophilic substitution is a reaction where a nucleophile replaces a leaving group in a molecule. In this scenario, the excess Cl- acts as a nucleophile that can attack the bromonium ion formed during the reaction, leading to the substitution of bromine with chlorine, which influences the final product distribution and the relative amounts of stereoisomers.
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Related Practice
Textbook Question
Show how each of the following compounds can be synthesized from an alkene:
a.
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Textbook Question
Show how each of the following compounds can be synthesized from an alkene:
b.
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Textbook Question
What stereoisomers would you expect to obtain from each of the following reactions?
c.
d.
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Textbook Question
What is the product of the reaction of maleate and H2O when H2SO4 is used as a catalyst instead of fumarase?
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Textbook Question
When Br2 adds to a cis alkene that has different substituents attached to each of the two sp2 carbons, such as cis-2-heptene, identical amounts of the two threo enantiomers are obtained even though Br- is more likely to add to the less sterically hindered carbon of the bromonium ion. Explain why identical amounts of the two enantiomers are obtained.
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