OChem2Ch10

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Author:
victimsofadown
ID:
202008
Filename:
OChem2Ch10
Updated:
2013-03-14 12:34:38
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OChem2Test1
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OChem2Ch10
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  1. What is the most common preparation of alkenes/alkynes?
    • Geminal or vicinal dibromide treated with a strong base (NaNH3 in NH3(l) at -33C).
    • This runs what is essentially an E2 rxn and forms the double bond (or triple bond if run again).
  2. Alkynes as acids
    • R-C=C-H 
    • H can be depronated by a strong base (stronger than oxybase eg NaNH3/NH3(l)) to beccome the acetylide ion R-C=C: 
    • Acetylide ion is fantastic base!
  3. Hydrogenation [alkyne]

    H2
    ----->
    Pt
    • Alkyne -> Alkene -> Alkane
    • Reacts too quickly to isolate alkene
    • Requires 2 equivalents of H2
  4. Hydrogenation [alkyne]

    H2
    -------->
    Lindlar's catalyst
    • Alkyne -> Cis Alkene
    • Syn addition
    • Cis alkene
    • NOTE: can also use Ni2B
  5. Dissolving Metal reduction [alkyne]

    Na
    ----->
    NH3 (l)
    • Alkyne -> trans alkene
    • Anti addition
    • Trans alkene only
    • NOTE - easy cleanup by evaporating solvent
  6. Hydrohalogenation  [alkyne]

    HBr
    ----->
    ROOR
    • Addition of H and BR across 3x bond
    • Anti-markovnikov
    • Both E and Z products
    • MECHANISM: radical
  7. Acid-catalyzed Hydration [alkyne]

    H2SO4, H2O
    --------------->
    HgSO4
    • Addition of OH and H across 3x bond
    • Markovnikov
    • Enol -> keto tautomerization (C=O not C=C)
    • No stereochemistry, typically used for terminal alkenes
    • NOTE - ideal conditions differ from alkene
  8. Hydroboration-oxidation [alkyne]

    1)BH3*THF
    ------------->
    2) HOOH, NaOH
    • Addition of OH and H across 3x bond
    • Anti-markovnikov
    • Enol -> keto tautomerization (C=O not C=C)
    • NOTE - terminal alkynes are too reactive for BH3 so (sia)2BH or 9-BBH must be used.  This converts the terminal alkynes to aldehydes.
  9. Halogenation [alkyne]

    Br2
    ------->
    CH3COOH, LiBr
    • Addition of Br and Br across 3x bond
    • Anti addition
    • Trans product
    • MECHANISM: Bromonium ion
    • NOTE - Cl will also work
    • NOTE - can be performed again on 2x bond
    • NOTE - CH3COOH+LiBr could also be CCl4
  10. Hydrohalogenation [alkyne]

    HBr
    ----->
    • Addition of Br and H across 3x bond
    • Markovnikov
    • MECHANISM: carbocation intermediate
    • NOTE - Cl will also work
    • NOTE - can be performed again on 2x bond
  11. Ozonolysis [alkyne]

    1) O3
    ----->
    2) H2O
    • INTERNAL - Cleavage of triple bond, yields two carboxylic acids
    • TERMINAL - Cleavage of triple bond, yields carboxylic acid and CO2
  12. Alkylation [alkyne]

    1) NaNH2
    ------->
    2) RX
    Replacement of H with R group

    • MECHANISM: removal of acidic H to create acetylide ion.  Ion acts as base in SN2 rxn.
    • NOTE- immensely important because it can create new c-c bonds!
    • NOTE- should be primary alkyl halide (SN2 reaction)
    • NOTE- acetylene can do this twice

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