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Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 8c
Chapter 7, Problem 8c

What alkene should be used to synthesize each of the following alkyl bromides?
c.

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1
Analyze the structure of the given alkyl bromide. The molecule consists of a cyclohexane ring attached to a carbon atom that is bonded to a bromine atom, a methyl group, and another methyl group.
Recall that alkyl bromides can be synthesized from alkenes via electrophilic addition of HBr. This reaction follows Markovnikov's rule, where the bromine atom adds to the more substituted carbon of the double bond.
Identify the carbon atom in the alkyl bromide where the bromine is attached. This carbon is tertiary, meaning it is bonded to three other carbon atoms. The alkene precursor must have a double bond between this carbon and one of its neighboring carbons.
Propose the structure of the alkene. To form the given alkyl bromide, the alkene should have a double bond between the tertiary carbon (where bromine is attached in the product) and the cyclohexane ring. The structure of the alkene would be 1-isopropylcyclohexene.
Explain the reaction mechanism. When HBr is added to the alkene, the proton (H⁺) adds to the less substituted carbon of the double bond (Markovnikov addition), and the bromine (Br⁻) adds to the more substituted carbon, resulting in the formation of the given alkyl bromide.

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Key Concepts

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

Alkenes and Their Reactivity

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond, which makes them more reactive than alkanes. This reactivity allows alkenes to undergo various chemical reactions, including electrophilic addition, where reagents add across the double bond. Understanding the structure and reactivity of alkenes is crucial for predicting the products of reactions and for designing synthetic pathways.
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Alkene Metathesis Concept 1

Electrophilic Addition Reactions

Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a nucleophile, typically involving alkenes. In this process, the double bond of the alkene acts as a nucleophile, attacking the electrophile, leading to the formation of a more stable product. This concept is essential for determining how to synthesize specific alkyl bromides from alkenes by identifying the appropriate electrophilic reagent.
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Synthesis of Alkyl Bromides

Alkyl bromides can be synthesized from alkenes through the addition of bromine or hydrogen bromide (HBr) to the double bond. The regioselectivity of this addition can be influenced by factors such as Markovnikov's rule, which states that the more substituted carbon will bond with the electrophile. Understanding the synthesis of alkyl bromides is key to solving the question, as it involves selecting the correct alkene that will yield the desired bromide product.
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Related Practice
Textbook Question

Answer the following questions about the mechanism for the acid-catalyzed hydration of an alkene:

a. How many transition states are there?

b. How many intermediates are there?

c. Which step in the forward direction has the smallest rate constant?

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Textbook Question

What alkene should be used to synthesize each of the following alkyl bromides?

b.

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Textbook Question

What is the major product obtained from the addition of HBr to each of the following compounds?

e.

f.

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Textbook Question

The pKa of a protonated alcohol is about -2.5, and the pKa of an alcohol is about 15. Therefore, as long as the pH of the solution is greater than _______ and less than _______, more than 50% of 2-propanol (the product of the reaction on p. 244) will be in its neutral, nonprotonated form.

1
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Textbook Question

What is the major product obtained from the addition of HBr to each of the following compounds?

a.

b.

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Textbook Question

What alkene should be used to synthesize each of the following alkyl bromides?

d.

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