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Questions and Answers
What happens to radical formation when chlorine is involved?
What happens to radical formation when chlorine is involved?
According to Hammond’s Postulate, what does the transition state resemble?
According to Hammond’s Postulate, what does the transition state resemble?
Which statement about bromine in radical reactions is true?
Which statement about bromine in radical reactions is true?
What is the expected outcome in a radical addition reaction involving alkenes and peroxides?
What is the expected outcome in a radical addition reaction involving alkenes and peroxides?
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Which of the following statements about fluorine and iodine radicals is correct?
Which of the following statements about fluorine and iodine radicals is correct?
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Why do radicals resist rearrangement compared to carbocations?
Why do radicals resist rearrangement compared to carbocations?
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What can be inferred about the radical addition of HBr compared to HCl and HI?
What can be inferred about the radical addition of HBr compared to HCl and HI?
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What is the result of removing a hydrogen atom from an asymmetric center in a radical reaction?
What is the result of removing a hydrogen atom from an asymmetric center in a radical reaction?
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What is the ratio of the predicted formation of 2-chlorobutane to 1-chlorobutane based on the relative reactivity?
What is the ratio of the predicted formation of 2-chlorobutane to 1-chlorobutane based on the relative reactivity?
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Which factor primarily influences the distribution of products in radical chlorination reactions?
Which factor primarily influences the distribution of products in radical chlorination reactions?
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In radical chlorination, how many equivalent hydrogen atoms are there in butane that can react?
In radical chlorination, how many equivalent hydrogen atoms are there in butane that can react?
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What property makes bromine radicals less reactive than chlorine radicals?
What property makes bromine radicals less reactive than chlorine radicals?
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How many unique products can result from the monochlorination of methylcyclohexane, excluding stereoisomers?
How many unique products can result from the monochlorination of methylcyclohexane, excluding stereoisomers?
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Given the reactivity values of 1°, 2°, and 3°, which is the least abundant product from the monochlorination of methylcyclohexane?
Given the reactivity values of 1°, 2°, and 3°, which is the least abundant product from the monochlorination of methylcyclohexane?
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What is the expected percentage yield of 1-chlorobutane compared to 2-chlorobutane based on calculations?
What is the expected percentage yield of 1-chlorobutane compared to 2-chlorobutane based on calculations?
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What is the primary factor that distinguishes the ability of alkanes to undergo radical chlorination versus bromination?
What is the primary factor that distinguishes the ability of alkanes to undergo radical chlorination versus bromination?
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Study Notes
Radical Chlorination of Alkanes
- There are six ways to form 1-chlorobutane and four ways to form 2-chlorobutane.
- The relative reactivity of primary, secondary and tertiary hydrogens to radical chlorination is 1:3.8:5.
Radical Stability and Rate of Formation
- Radicals are not as strongly stabilized by hyperconjugation as carbocations.
Regiochemistry of Radical Chlorination
- The relative reactivity of a particular hydrogen and the probability that hydrogen collides and reacts determines the regiochemistry of a radical halogenation reaction.
Radical Bromination
- Bromine radicals are less reactive than chlorine radicals because the H-Br bond (88 kcal/mol) is weaker than the H-Cl bond (103 kcal/mol) formed in chlorination.
- This leads to greater radical selectivity in the formation of the more stable radical.
- The reactivity-selectivity principle states that radical formation is exothermic with chlorine and endothermic with bromine.
- The Hammond’s Postulate: The transition state more strongly resembles the higher energy species (starting material or product).
Stereochemistry of a Radical Substitution Reaction
- A new asymmetric center is formed, and the product is a racemic mixture.
Utility of Peroxides: Anti-Markovnikov Addition
- Haloacids add to alkenes to give the more substituted halide.
- In the presence of a peroxide, the less substituted halide is preferred.
- The peroxide is cleaved in the first initiation step, and the resulting alkoxy radicals abstract hydrogen from H-Br to yield Br radicals, which propagate the chain reaction.
- This is known as the anti-Markovnikov addition of HBr to alkenes
Stereochemistry of a Radical Addition Reaction
- A new asymmetric center is formed, and the product is a racemic mixture.
Radicals Resist Rearrangement
- Carbocations readily rearrange. Radicals, with their half-filled p-orbitals, rarely exhibit migration of hydrogen or ordinary alkyl groups.
Radical Addition of HBr is Unique
- HCl and HI exhibit Markovnikov addition with or without peroxide.
Bromine Radicals Hit the Sweet Spot
- Bromine radicals are reactive enough to make the reaction happen, while still being selective enough to form the more thermodynamically stable radical, making it unique.
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Description
This quiz covers the key concepts of radical chlorination and bromination of alkanes, including the formation of 1-chlorobutane and 2-chlorobutane. It delves into the stability of radicals, regiochemistry, and the principles governing the reactivity and selectivity of chlorine and bromine radicals. Test your understanding of these important organic chemistry principles.
