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orgo question

Discussion in 'DAT Discussions' started by ippie, May 11, 2008.

  1. ippie

    ippie ippie

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    picture attached for the following questions.


    #1. what is the name of the given compound?

    #2. what product result?
    a) 2-ethoxy butane
    b) 2-ethoxypropane
    c) 2-ethoxy-1propanol
    d) 3-ethoxy-2-propanol
    e) 1-ethoxy-2-propanol
     

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  3. 4-methoxy-1-chlorocyclohexane

    1-ethoxy-2-propanol
    Protonation followed by an SN2 like addition of ethanol (since epoxide is secondary and primary), deprotonation of ethanol to give ethoxide substituent.
     
  4. americanpierg

    americanpierg Senior Member

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    Hmm...you posted this exact same question a week ago.

    Unless its trisubstituted, the epoxide will break with the addition occuring on the less substituted carbon, in this case carbon 1, with C being the right answer
     
  5. Check your nomenclature. You doing the problem right in that it adds to the least substituted carbon.

    I scanned what I got but had to do it at a ridiculous low quality, hopefully you can still get what I had. But you number from the ethoxy substituent since the hydroxyl group is dead center of the propane backbone.

    The web page is also the structure for 1-ethoxy-2-propanol
     

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  6. ippie

    ippie ippie

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    americanpierg! If you add ethoxy group to the less substituted carbon, then you have the answer #d (not #c). right? But the answer key said the answer is #c.
    joh020340! the answer is #c.
    But I am sure the answer is #d. that's why I uploaded this question. This question is from Organic Chemistry Odyssey.
     
  7. Well you guys can argue all you want but I'm 100% sure that it's E no matter what the answer key says. C would come from a tertiary carbon on the left, which it isn't (would form a tertiary carbocation intermediate, followed by addition of ethanol). D is not even a possible compound because its nomenclature is wrong. If you want to accept either C or D as a right answer, go ahead, although I suggest you review an actual Organic Chemistry textbook for factual mechanisms and nomenclature, not a review book. A secondary and primary epoxide treated in acidic solution cleaves in a manner where the oxygen (from the epoxide) goes to the more substituted (secondary here) carbon because the nucleophile (ethanol) will attack at the least substituted carbon. If your answer based on drawings looks like that thumbnail above, then E is right because 1: that's just how you name molecules, and 2: thats exactly what i searched for and the website listed it as. Like I said before, take my opinion or leave it, but if you do not believe me, look at a credible resource, not a review book or a website.
     
  8. la brat

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    I respectively disagree, joh. Ethanol, the nucleophile, attacks the the more substituted carbon in the presence of acid; the H3O+ protonates the epoxide which puts the partial positive charge on the secondary carbon before the nucleophile even arrives; this kind of reaction is partial SN1/SN2. Therefore, the major product should have an alkoxy group at the secondary position, not primary, once the alcohol deprotonates. If the solvent was basic like ethoxy ion, then you would be right. This is straight out of my textbook. Could it be wrong?
     
  9. ippie

    ippie ippie

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    According to my orgo textbook "McMurry", under basic condition, ethoxy attacks the less substituted carbon. However, be careful when it's under acidic condition! Under acidic condition, if you have primary and secondary carbon, ethoxy attacks the less substituted carbon same as in basic condition, but if you have tertiary carbon, ethoxy attacks the more substituted carbon.
    In the question, we see only primary and secondary carbon under acidic condition. That's why I think the answer is #d. Isn't it? Solomon shows us only the example of tertiary carbon under acidic condition. That's whay most students think that under acidic condition, the more substituted carbon is attacked, but Solomon doesn't show us primary and secondary carbon under acidic condition. Any other opinion???
     
  10. la brat

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    Then, Ippie, our textbooks must differ. Maybe this is one of those organic chemistry grey areas. More than once it mentions that under acid conditions, nucleophile attacks more substituted carbon on epoxide ring. I bet most of problems given probably do involve tertiary carbons though
     
  11. I agree with your mechanism but not with the nomenclature. I still think that the carbon attached to the ethoxy substituent becomes the C1. It doesn't make sense for it to be a 3 when the hydroxy is in the middle of the propane chain. With either end being 1 carbon away from the alcohol, the carbon with the substituent becomes the C1 to give the substituent the lowest possible number.
     
  12. Yes but only when it can form a tertiary carbocation (only with disubstituted epoxide).
     
  13. la brat

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    Well Joh, I guess you'll just have to take this up with prof. Bruice who wrote my textbook. It contains this exact problem with the major product being the secondary alkoxide substituent/ primary alcohol. Plus, according to Ippie's answer key, C is the correct answer.
     
  14. Well funny how things work cause I have the exact opposite in my book. You can take it up with McMurry and both profs I had. Like I said, you guys can accept that as your answer but I will not. Besides, what's the worst that can happen, 1 question wrong on the DAT even if they have it as a question. Also, review books and DAT practice tests are known for having mistakes, that is why you must consult textbooks if you disagree. So it is possible the the answer key is wrong, key word here being POSSIBLE (and I believe probable).
     

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