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Free Radical Reactions

Free Radical Reactions. Radical Reactions Chapter 10. Description Causes of Free Radical Formation Importance in Biology, Medicine & Industry Mechanism Selectivity of Halogens Anti-Markovnikov Reaction Ozone Depletion & CFC’s. Description.

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Free Radical Reactions

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  1. Free Radical Reactions

  2. Radical Reactions Chapter 10 • Description • Causes of Free Radical Formation • Importance in Biology, Medicine & Industry • Mechanism • Selectivity of Halogens • Anti-Markovnikov Reaction • Ozone Depletion & CFC’s

  3. Description Molecules or Atoms that contain an unpaired electron. . CH3

  4. Description Heterolysis or Heterolytic Leads to Ion formation

  5. Description Homolysis or Homolytic Cleavage Leads to Free Radical formation

  6. Description Stabilization- The greater the ability to spread out the burden of the free radical the more stable the compound.

  7. Causes of Free Radical Formation • Metabolism • Immune Response • Combustion • Radiation • UV (Sunlight) • Environmental Pollutants

  8. Importance in Biology & Medicine • Aging(Link 2) • Cancer • Emphysema • Nitric Oxide • Blood Pressure Regulation • Blood Clotting • Neurotransmission • Immune Response • Metabolism • Wrinkles • Etc.

  9. Importance in Biology & Medicine • Antioxidants - absorb free radicals • Vitamin E • Vitamin C • Beta-carotene • Selenium • Lycopene • Melatonin(Link 2) Source: http://www.biochem.wisc.edu/biochem510/slides/20antiox1.pdf

  10. Importance in Biology & Medicine Source: http://www.biochem.wisc.edu/biochem510/slides/20antiox1.pdf

  11. Importance in Industry • Polymers (Plastics) • Polyethylene • Telfon • Polystyrene • Combustion • Cracking

  12. Mechanism Three major Steps • Chain Initiation Step (Initiation) • Chain Propagation Steps (Propagation) • Chain Termination Steps (Termination)

  13. Mechanism

  14. Mechanism Chain Termination

  15. Selectivity of Halogens

  16. Selectivity of Halogens

  17. Selectivity of Halogens Source:http://library.kcc.hawaii.edu/external/chemistry/electronegativity.html

  18. Selectivity of Halogens • Reactivity • Fluorination > Chlorination > Bromination > Iodination • Higher the reactivity the lower the selectivity. • The decrease in electronegativity explains the decrease in reactivity and thus increase in selectivity.

  19. Selectivity of Halogens

  20. Selectivity of Halogens Ea Collision < 10% > 90%

  21. Selectivity of Halogens Ea Collision < 10% > 90%

  22. Anti-Markovnikov Reaction • Free Radical Reaction • Ea Driven Reaction

  23. Anti-Markovnikov Reaction

  24. Anti-Markovnikov Reaction

  25. Markovnikov vs. Anti-Markovnikov • Both reactions are Ea driven • In Markovnikov addition the hydrogen adds first • leading to the most stable carbocation. • In anti-Markovnikov addition the Bromine adds first • leading to the most stable free radical.

  26. Natural Ozone Reactions Source: http://www.atmos.umd.edu/~owen/METO123/OZHOLE/lecture.html

  27. Natural Ozone Reactions Source: http://www.atmos.umd.edu/~owen/METO123/OZHOLE/lecture.html

  28. Natural Ozone Reactions Natural stratospheric ozone equilibrium. Step 1: O2 +UV(180-240nm) ==> O + OStep 2: O + O2 + M ==> O3 + M* (Produces ozone from oxygen) Step 3: A) O3 + UV(200-320nm) ==> O +O2 B) O +O3 ==> 2 O2(Produces oxygen from ozone) An equilibrium concentration of ozone occurs

  29. Ozone Depletion & CFC’s • CF2Cl2 + hv CF2Cl. + Cl. • Cl.+ O3 ClO. + O2 • ClO. + O O2 + Cl.

  30. Problems (p.459, 460, 461) • 10.2 • 10.4 • 10.6 • 10.8

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