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Chapter 9 Reactions of Alkanes Radicals

Chapter 9 Reactions of Alkanes Radicals. Irene Lee Case Western Reserve University. Alkanes are very unreactive compounds because . However, alkanes do react with Cl 2 and Br 2. they have only strong s bonds and atoms with no partial charges. Reaction of Alkane with Cl 2 or Br 2.

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Chapter 9 Reactions of Alkanes Radicals

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  1. Chapter 9 Reactions of Alkanes Radicals Irene Lee Case Western Reserve University

  2. Alkanes are very unreactive compounds because However, alkanes do react with Cl2 and Br2 they have only strong s bonds and atoms with no partial charges

  3. Reaction of Alkane with Cl2 or Br2

  4. Factors that determine product distribution … The rate-determining step of the overall reaction is hydrogen abstraction

  5. Consider the relative stabilities of alkyl radicals, The stable alkyl radical is formed faster, therefore 2-chlorobutane is formed faster

  6. pg 341 middle

  7. In determining the relative amounts of products obtained, both probability and reactivity should be considered probability: the number of hydrogens that can be abstracted that will lead to the formation of the particular product reactivity: the relative rate at which a particular hydrogen is abstracted

  8. The Reactivity–Selectivity Principle A bromine radical is less reactive and more selective than a chlorine radical

  9. Why are the relative rates of radical formation so different between the bromine versus the chlorine radical?

  10. The more reactive a species is, the less selective it will be

  11. What about fluorination and iodination? Alkanes undergo chlorination and bromination, but not iodination Fluorination is too violent of a reaction to be useful

  12. Consider the relative stabilities of radicals

  13. Radical Substitution of Benzylic Hydrogens The more stable radicals form faster

  14. Because of the reactivity of allylic hydrogens, a milder brominating reagent can be used A very important and useful reaction

  15. Stereochemistry of Radical Substitution Reactions

  16. Why are both enantiomers formed? Consider the first propagation step

  17. What happens if the reactant already has an asymmetric carbon and the radical substitution reaction creates a second asymmetric carbon?

  18. Radical Reactions in Biological Systems Liver enzymes & cytochrome P450

  19. Radical Inhibitors/ Antioxidants BHA & BHT: are synthetic chemicals “bad”?

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