Free Radical Reactions

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Presentation transcript:

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 Molecules or Atoms that contain an unpaired electron. . CH3

Description Heterolysis or Heterolytic Leads to Ion formation

Description Homolysis or Homolytic Cleavage Leads to Free Radical formation

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

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

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

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

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

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

Mechanism Three major Steps Chain Initiation Step (Initiation) Chain Propagation Steps (Propagation) Chain Termination Steps (Termination)

Mechanism

Mechanism Chain Termination

Selectivity of Halogens

Selectivity of Halogens Reaction Name First Chain Propagation Reaction Enthalpy Overall Enthalpy Fluorination F. + CH4 -130 -432 Chlorination Cl. + CH4 +8 -101 Bromination Br. + CH4 +74 -26 Iodination I. + CH4 +142 +53

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

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.

Selectivity of Halogens

Selectivity of Halogens Ea Collision < 10% > 90%

Selectivity of Halogens Ea Collision < 10% > 90%

Anti-Markovnikov Reaction Free Radical Reaction Ea Driven Reaction

Anti-Markovnikov Reaction

Anti-Markovnikov Reaction

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.

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

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

Natural Ozone Reactions Natural stratospheric ozone equilibrium. Step 1: O2 +UV(180-240nm) ==> O + O Step 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

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

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