CHM 326: Exam Mechanisms

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  1. Allylic bromination with NBS
    • Alkene + NBS, HBr trace, hv
    • Usually in carbon tetrachloride
    • Free radical mechanism
  2. Allylic bromination
    • Alkene + low conc. Br2, hv
    • Free radical mechanism
  3. Nucleophilic substitution of allylic halides (SN1)
    • Alkene + H2O or HOR, heat
    • Involves carbocation intermediate
  4. Nucleophilic substitution of allylic halides (SN2)
    Allylic systems more reactive because of stabilization of the transition state
  5. Electrophilic aromatic substitution
    • Reactants: Aromatic + strong E + Base
    • Intermediate: Endothermic, nonaromatic (base takes hydrogen adjacent to E)
    • Product: Ectothermic, aromatic with E , H-Base
  6. Bromination of an aromatic
    • Reagents: Br2, FeBr3
    • Electrophile: Br-Br+-FeBr3
    • Product: aromatic ring with Br
  7. Chlorination of an aromatic
    • Reagents: Cl2, AlCl3 or FeCl3
    • Electrophile: Cl-Cl+-Al-Cl3 or Cl-Cl+-FeCl3
    • Product: aromatic ring with Cl
  8. Iodination of an aromatic
    • Reagents: I2, HNO3
    • Electrophile: I+
    • Product: aromatic ring with I
  9. Nitration of an aromatic
    • Reagents: HNO3, H2SO4
    • Electrophile: O=N+=O
    • Product:
  10. Sulfation of an aromatic
    • Reagents: SO3, H2SO4
    • Electrophile: SO3
    • Product:
    • (After sulfuric acid ion takes H, another sulfuric acid adds H to the benzenesulfonic acid ion)
  11. Nitro group reduction of an aromatic
    • Reagents: Zn or Sn or Fe and HCl
    • Intermediate: aromatic ring with N+H3
    • Product:
  12. Friedel-Crafts Alkylation
    • Reagents: R-X, AlCl3 or FeBr3
    • Electrophile: R+
    • Product: Aromatic ring with R substituent (HX + AlCl3)

    • To get R+:
    • R-X + AlCl3 ⇌ R-X+-Al-Cl3 ⇌ R + X-Al-Cl3
    • Base: X-Al-Cl3

    Note: rearragements of the R group is possible because of the cation
  13. Friedel-Crafts Acylation
    • Reagents:
    • 1) and AlCl3
    • 2) H2O
    • Electrophile: R-C≡O+
    • Product:



    Note: AlCl3 binds to O after acylium ion binds to benzene so H2O is needed in second step to kick Al off
  14. Ortho-para ratio
    • Probability: Ortho favored (2 ortho position vs 1 para position)
    • Steric hindrance: Para favored if substituent on ring or electrophile is large
  15. Orientation when there are two or more substituents
    • 1) Reinforce each other's orienting effects
    • 2) Oppose each other's orienting effects (activator or better nuc dominates but if they are similar, mixtures result)
    • 3) When substituents meta to one another, electrophile usually won't go in between them

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Author:
 omi14
ID:
 132583
Filename:
 CHM 326: Exam Mechanisms
Updated:
2012-02-03 05:45:33
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organic chemistry ii exam
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For CHM326 Organic Chemistry
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