Alkyl Halide Reactions

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Author:
lukemlj
ID:
51301
Filename:
Alkyl Halide Reactions
Updated:
2010-11-23 07:26:32
Tags:
alkyl halide reactions sn1 sn2
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Description:
alkyl halide reactions sn1 sn2
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  1. SN2 stands for
    substitution, nucleophile, bimolecular
  2. What effect does an SN2 reaction have on stereochemistry?
    Configuration is inverted (e.g. R to S or vice versa)
  3. SN2 Substrate
    • Most reactive with methyl, primary, and sometimes secondary.
    • Will not react with tertiary, vinylic halides and aryl halides.
  4. SN2 Nucleophile
    • Nucleophilicity roughly parallels basicity
    • Usually increases going down periodic table
    • Usually negatively charged nucleophiles are more reactive than neutral ones
  5. SN2 Leaving Group
    • Good leaving groups stabilize the negative charge:
    • TosO, I, Br, Cl
    • Poor leaving groups:
    • OH, NH2, OR, F
  6. SN2 Solvent
    • Polar aprotic solvents are the best for SN2
    • Good solvents include:
    • HMPA, CH3CN, DMF, DMSO
  7. The SN1 reaction occurs through....
    A carbocation intermediate
  8. What effect does an SN1 reaction have on stereochemistry?
    Theoretically no effect, except that racemic products are not exactly 50/50 due to ion pairs getting in the way.
  9. SN1 Substrate
    • Stability of the carbocation increases reaction rate:
    • Tertiary > Secondary = Benzylic = Allylic
  10. SN1 Leaving Group
    • Often carried out in acidic conditions.
    • Good: TosO, H2O, I > Br > Cl > OH
  11. SN1 Nucleophile
    Does not effect reaction since it does not take part in the rate-limiting step
  12. SN1 Solvent
    • Stabilizes transition state, not reactant.
    • Strong polar solvents are good: Water

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