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Double checking organic chem mechanisms

  1. Aug 21, 2007 #1
    Hello,

    I need to make sure I understand some of the reactions correctly... For example:

    CH2OHCH3 in H+ will give us CH2=CH2. I would think that here the H+ bonded with the OH resulting in H2O (a leaving group), but I am not sure what happens to the other leaving H.

    In RC≡CR' in Na/NH3, we get RCH=CHR' in an anti addition. Where did the 2 H come from? The NH3?

    RCH=CH2 in H3O+ gives RCHOHCH3. Did the OH and H come from the H3O+? Do we then have one last H that does not bond with the molecule? And did the OH add to the C bonded with the R because it is the most substituted carbon?

    In RCH=CH2 in (1) Hg(OAc)2/H2O and (2) NaBH4, NaOH, we get RCHOHCH3. Where did the OH and H come from? Did the OH add to the C bonded with the R because it is the most substituted carbon?

    In RCH=CH2 in (1) BH3/THF and (2) H2O2/OH- we get RCH2CH2OH. Did the OH add to the C because it was the least substituted? Also, is the mechanism the following: first, Br (from BH3) bonds with the least subst. carbon, and H also from BH3 adds to the other C, thus breaking the double bond. Then in step (2) Br is replaced by OH, from OH-.

    And finally:
    a) ROH + SOCl2 -> RCl
    and
    b) ROH + TsCl ---(base)--> ROTs

    These 2 reactions confuse me. I thought that in a) the H would bond with a Cl giving HCl + RSOCl. Why does it give RCl?
    However in b) what I thought would happen in a) does take place. H and Cl bond, resulting in ROTs. Why?

    Thank you so much for your help, I hope I was clear enough!
     
  2. jcsd
  3. Aug 21, 2007 #2

    Gokul43201

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    The acid is H+A-. The other H atom (through a carbocation mechanism) goes away with the conjugate base, A-
     
  4. Aug 21, 2007 #3
    Thanks!
     
  5. Aug 22, 2007 #4

    Gokul43201

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    Yes, one H-atom from each NH3.

    Yes, yes and yes. Look up the mechanism for electrophilic addition to alkenes through carbocation formation on the most substituted carbon.
     
  6. Aug 23, 2007 #5
    Thank you so much, you're so helpful!
    We rarely get the mechanisms in class, as we are told we have to do a lot of memorization. But I found that understanding the mechanism allows me to remember the reactions for the rest of the semester, instead of relying on memorization.
     
  7. Aug 24, 2007 #6

    Gokul43201

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    You will find these mechanisms in any standard O Chem text. In Morrisson & Boyd (6th Ed.), this is in Ch 9: Reactions of Alkenes.
     
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