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Sn1, E1, Sn2, E2

Discussion in 'DAT Discussions' started by Dencology, May 29, 2008.

  1. Dencology

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    guys i am going crazy over this stuff. anyone out there has a good way of explaining when to go either way. i know the general basic for sn1, sn2, ... but i still get some questions wrong which i should nailed them. any help?
     
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  3. userah

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    I'll break it down

    Sn1
    - 3*>2*>1*
    - Prefer polar protic solvents (water,methanol, etc)
    - Only dependent on the LG (not the nucleophile)
    - Formation of carbocation intermediate
    - Because it forms carbocation intermediate, Nu can attack from top or bottom, so you get racemic mixtures (thus you have optical inactivity)
    - Achiral intermediate

    E1
    - Pretty much same as everything stated for Sn1
    - Hard to really differentiate between E1 products and Sn1 products although kaplan says E1 preferred at higher temperatures

    Sn2
    - 1*>2*>3*
    - Prefer polar aprotic solvents (DMSO, etc) (lack acidic hydrogens)
    - Bimolecular, so dependent on LG and Nu
    - Inversion of products because of backside attack by Nu (basically it switches config. S becomes R or R becomes S)
    - Product is optically active
    - Best Nu are basic atoms

    E2
    - Easier to differentiate between Sn2 and E2
    - E2 is not sterically hindered like Sn2 so it can attack tertiary carbons as long as you have a STRONG BASE
    - So if you see a strong base and a tertiary alkyl halide think E2.

    that's all i can think of for now. maybe if you tell me what kind of problems you're having trouble with, i can be of more help.
     

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