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Ch.8 - Reactions of Alkenes
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.8 - Reactions of AlkenesProblem 18c,d
Chapter 8, Problem 18c,d

Propose mechanisms and predict the major products of the following reactions. Include stereochemistry where appropriate.
(c) (E)-dec-3-ene + Br2 in CCl4
(d) (Z)-dec-3-ene + Br2 in CCl4
Problem-Solving Hint: Models may be helpful whenever stereochemistry is involved. Write complete structures, including all bonds and charges, when writing mechanisms.

Verified step by step guidance
1
Step 1: Recognize the reaction type. The addition of Br2 to an alkene in a non-polar solvent like CCl4 is a halogenation reaction. This reaction proceeds via a cyclic bromonium ion intermediate, followed by nucleophilic attack by the bromide ion.
Step 2: Analyze the stereochemistry of the starting alkene. For part (c), the alkene is (E)-dec-3-ene, meaning the substituents on the double bond are trans to each other. For part (d), the alkene is (Z)-dec-3-ene, meaning the substituents on the double bond are cis to each other.
Step 3: Draw the mechanism for the reaction. Begin by showing the π electrons of the alkene attacking one bromine atom in Br2, forming a cyclic bromonium ion intermediate. Represent the stereochemistry of the alkene accurately in this step.
Step 4: Show the nucleophilic attack by the bromide ion on the bromonium ion intermediate. The attack occurs from the opposite side of the cyclic bromonium ion (anti-addition), leading to the formation of a vicinal dibromide. Ensure stereochemistry is properly depicted in the product.
Step 5: Predict the major product for each reaction. For (E)-dec-3-ene, the anti-addition of bromine will result in a product with trans stereochemistry. For (Z)-dec-3-ene, the anti-addition of bromine will result in a product with cis stereochemistry. Confirm the stereochemical outcomes by considering the spatial arrangement of substituents in the starting alkene and the anti-addition mechanism.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrophilic Addition Reactions

Electrophilic addition reactions involve the addition of an electrophile to a nucleophile, typically across a double bond. In the case of alkenes like (E)-dec-3-ene and (Z)-dec-3-ene, the π bond acts as a nucleophile, reacting with bromine (Br2) as the electrophile. This reaction leads to the formation of a vicinal dibromide product, where bromine atoms are added to adjacent carbon atoms.
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Stereochemistry and Isomerism

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the context of (E) and (Z) isomers, the configuration around the double bond influences the outcome of the reaction. Understanding stereochemistry is crucial for predicting the major products, as the addition of bromine can lead to different stereoisomers depending on the starting alkene's configuration.
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Mechanism of Bromination

The mechanism of bromination involves the formation of a bromonium ion intermediate when Br2 approaches the alkene. This intermediate is crucial for determining the stereochemistry of the final product, as it leads to a backside attack by a bromide ion, resulting in anti-addition. This process is essential for accurately predicting the major products and their stereochemical configurations in the reactions of (E)- and (Z)-dec-3-ene.
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Related Practice
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