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AAMC Organic Chem Mechanism Question?

Discussion in 'MCAT Study Question Q&A' started by stester77s, 05.19.14.

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  1. stester77s

    stester77s 2+ Year Member

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    I attached an image of the mechaism in question. My question, is how does the middle oxygen get protonated while the other oxygen has a negative charge? Shouldn't the oxygen with the negative charge get protonated before the neutral oxygen?


    What is the name of this synthesis (so I can look up alternative mechanisms)?
     

    Attached Files:

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  3. tdod

    tdod 2+ Year Member

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    my best answer is that the alkoxide oxygen probably does pick up a proton first. however, there is no way to break up the compound, so eventually that proton gets lost. in contrast, when the central oxygen picks up a proton, the compound can collapse and will not reform.
     
  4. syoung

    syoung MS-3 5+ Year Member

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    Actually that mechanism looks weird on a couple of levels. What's the solvent? That would determine how the mechanism proceeds.
     
  5. SuperSneaky24

    SuperSneaky24

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    So my guess is that what you said also occurs (that the negative oxygen is protonated instead). What you'll get is both forms, kind of like a keto-enol tautomerization but not exactly the same. It is the form in the image that is reactive and will cause the forward reaction to occur.

    http://chemwiki.ucdavis.edu/Organic...d_Anhydrides_React_with_Amines_to_Form_Amides
    Found the reaction online, except that hydride shift never occurs, so it's probably not that critical of a step
     
    syoung and DrknoSDN like this.
  6. DrknoSDN

    DrknoSDN

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    Nice, I was about to repost the same link as you. It does show a better mechanism.

    To find lots of mechanism pictures just search google images and type all the functional groups... I.E. "Anhydride Amine Amide", pops right up.
     

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