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AAMC 7 Question 169 OCHEM

Discussion in 'MCAT Discussions' started by OCPreMed, Aug 13, 2006.

  1. OCPreMed

    OCPreMed Member
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    Alright, my question is, Hydroxyl groups are always at 3400 ish and Carbonyls around 1700 ish on IR spectrum right????

    WELL, on my TPR test, the back of the book has the answers to the test and there is a discrepancy b/w the answer in the back and the answer online on their student tools.

    my buddy who is in an ochem lab, says that in a conjugated cycloalkane system, the carbonyl is at 3400, and hydroxyl is at 1700... I thought he was being an idiot until we checked the answers in the back of the test, and his answer was right and mine was wrong. THEN I go online and log into their student tools, and for 7r 169 they say that 'hydroxyl 3400 and carbonyl is 1700'. I don't know if I just went in a complete circle, but any help would be nice...
     
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  3. supafield

    supafield Dream Big
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    Princeton taught me 1650-1700 for double bonds and carbonyls.... 3500 for OH... that's what I'm going with

    Conjugated double bonds are different... stronger absorptions... but specific values... I was never given
     
  4. Pdiddy310

    Pdiddy310 Path = Fun
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    the OH functional group produces a broad spectrum b/n 3200-3600 while a carbonyl produces a sharp spectrum around 1700
     
  5. OCPreMed

    OCPreMed Member
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    even on a conjugated ring system??
     
  6. xylem29

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    Trust in Jordan and Jon :) - Carbonyls ALWAYS absorb at 1700 (or close to it) and OH ALWAYS at 3300-3500 range. Keep it simple folks - MCAT tests basic concepts, unless the passage tells you that conjugated systems reverses the IR absorption for alcohols and carbonyls, TPR made a typo.
     
  7. RPedigo

    Physician Faculty Moderator Emeritus 10+ Year Member

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    What are you talking about? Question 169 doesn't even have a "conjugated ring system". Compound 8 is FAR from conjugated. There are zero resonance forms that leave everything with a full octet.
     
  8. GeoMay22

    GeoMay22 Junior Member
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    I think I may have a more direct answer to your question. I had the same problem when I took TPR last april. Apparently there is a misprint in the back of the test that they give out. My teacher told us that the answers online were correct.
     
  9. OCPreMed

    OCPreMed Member
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    hey thanks about that geo, and RPedigo, it IS conjugated, its not aromatic though, i think you are confusing the two. conjugation is not the same thing as aromaticity...
     
  10. RPedigo

    Physician Faculty Moderator Emeritus 10+ Year Member

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    I'm an organic chemist, and I'll bet my life that Compound 8 is not conjugated.
     
  11. OCPreMed

    OCPreMed Member
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    you are right! it is not conjugated. The OH is allylic though. Sorry for the confusion and now I know who to ask ochem questions.. I'm an immunologist, not an ochemist.
     
  12. RPedigo

    Physician Faculty Moderator Emeritus 10+ Year Member

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    haha no problem... as long as we all know our stuff for Saturday, that's what counts.


    Good luck
     
  13. akinf

    akinf Senior Member
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    That question has to be wrong.
     
  14. MahSpoon

    MahSpoon is TOOOOO big
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    I'm in TPR course and we took 7, not 7R this past weekend. The back of my book matches the solutions they have and it says:

    169. D. Hydroxyl groups appear in the 3200–3600 cm–1 range of an IR spectrum, while carbonyl groups appear near 1700
    cm–1.

    I've taken Ochem and this is correct. Your buddy should probably get things straightened up otherwise he's in a world of hurt when trying to analyze IR specs.
     

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