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Radical reactions Forming of a radical

Radical reactions Forming of a radical. Homolysis:. Radical reactions Forming of a radical. Homolytic cleavage by Photolysis. Radical reactions Forming of a radical. Reactions of molecules with other radicals. Radical reactions Forming of a radical. Radical reactions Stability.

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Radical reactions Forming of a radical

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  1. Radical reactionsForming of a radical

  2. Homolysis: Radical reactionsForming of a radical

  3. Homolytic cleavage by Photolysis Radical reactionsForming of a radical

  4. Reactions of molecules with other radicals Radical reactionsForming of a radical

  5. Radical reactionsStability

  6. Radical substitution reactionsHalogenation

  7. Radical substitution reactionsHalogenation Chlorine rather unselective !!! (number of hydrogens versus radical position) Bromine less reactive- More selective !!!

  8. Stereochemistry: Radical substitution reactionsHalogenation

  9. Allylic and benzylic substitution Radical substitution reactionsHalogenation

  10. Allylic radical substitution Radical substitution reactionsHalogenation If polar solvent -> electrophilic addition (stabilization of carbocation) • If apolar solvent -> radical substitution • If low Br2 concentration -> allylic radical substitution • If high Br2 concentration -> radical addition to double bond

  11. Allylic radical substitution Radical substitution reactionsHalogenation If substrate not chosen carefully -> 3 products

  12. Allylic radical substitution -> NBS is better reagent if selective bromination wanted (in apolar solvent) NBS keeps concentration of Br2 low -> just allylic radical substitution (no radical addition to double bomd) Radical substitution reactionsHalogenation

  13. Benzylic radical substitution -> NBS is better reagent if effective bromination wanted Radical substitution reactionsHalogenation Cl2 is more reactive than Br2 -> chlorination can occur at different positions

  14. Radical addition reactionsAddition of HBr to alkenes

  15. Radical addition reactionsAddition of HBr to alkenes

  16. Addition to conjugated dienes Radical addition reactionsAddition of HBr to alkenes

  17. Radical polymerization reactionspolymerization of alkenes

  18. Radical polymerization reactionspolymerization of alkenes

  19. Radical addition reactionAddition of oxygen -> autooxidation

  20. Radical addition reactionAddition of oxygen -> autooxidation

  21. Autooxidation of unsaturated fats and oils -> origins of rancidity (unpleasant smell and taste of badly stored fats Radical addition reactionAddition of oxygen -> autooxidation

  22. Autooxidation of unsaturated fats and oils -> origins of rancidity (unpleasant smell and taste of badly stored fats Radical addition reactionAddition of oxygen -> autooxidation -> Oxidation (acid) and chain shortening

  23. Antioxidants and health Radical addition reactionAddition of oxygen -> autooxidation Vitamin E

  24. Many natural products are produced that way -> Enzymes (oxidases, peroxidases,…) catalyze reactions Radical reactionsPhenolic oxidative coupling

  25. Many natural products are produced that way -> Enzymes (oxidases, peroxidases,…) catalyze reactions Radical reactionsPhenolic oxidative coupling

  26. Electrophilic ReactionsAromatic substitution Electrophilic reactions with aromatic substrates -> substitution

  27. Electrophilic ReactionsAromatic substitution Halogenation

  28. Electrophilic ReactionsAromatic substitution Nitration

  29. Electrophilic ReactionsAromatic substitution Sulfonation

  30. Electrophilic ReactionsAromatic substitution Electrophilic alkylations -> Friedel-Craft alkylation

  31. Electrophilic ReactionsAromatic substitution Electrophilic alkylations -> Friedel-Craft alkylation -> Reaction mechanism dependent on structure of alkyl

  32. Electrophilic ReactionsAromatic substitution Electrophilic alkylations -> Friedel-Craft alkylation -> alkylation of aromatic ring can be achieved by any system that generates carbocation

  33. Electrophilic ReactionsAromatic substitution Electrophilic alkylations -> Friedel-Craft alkylation -> Limitation of alkylation by rearrangement reaction of carbocation

  34. Electrophilic ReactionsAromatic substitution Electrophilic acylation -> Friedel-Craft Acylation

  35. Electrophilic ReactionsAromatic substitution Electrophilic acylation -> Friedel-Craft Acylation

  36. Electrophilic ReactionsAromatic substitution Effect of substituents -> influence rate and position of substitution Electron withdrawing substituents -> deactivate and hinder further substitution (-> destabilize ortho and para -> substitution preferable in meta position) Electron donating substituents -> activate for further substitution (-> preferable in ortho and para) Substituent has maximum effect on reaction if it is in ortho or para position -> electron releasing substituents (ortho and para) -> electron withdrawing substituents (destabilize arenium cation ->meta)

  37. Electrophilic ReactionsAromatic substitution Effect of substituents -> influence rate and position of substitution

  38. Electrophilic ReactionsAromatic substitution Effect of substituents -> Inductive effect Nitration of Toluene -> E = NO2 Nitration of Toluene -> 59% ortho, 37% para, 4 % meta Nitration of Nitrobenzene -> 93% meta, 6% ortho, 1% para

  39. Electrophilic ReactionsAromatic substitution Effect of substituents -> Resonance Effect -> substitutents with strong electron releasers

  40. Electrophilic ReactionsAromatic substitution Effect of substituents

  41. Electrophilic ReactionsAromatic substitution Effect of substituents -> reaction is regioselective

  42. Electrophilic ReactionsAromatic substitution Converting substituents (introduced by electrophilic substitution) -> into other functional groups

  43. Electrophilic Reactionssubstitution on polycyclic aromatic compounds Monosubstitution -> predominant at position 1 Effect of substituents on further substitution Electron releasing substituent Electron withdrawing substituent

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