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AAMC 10/Organic Chem book discrepancy

Discussion in 'MCAT Study Question Q&A' started by tmh, Aug 14, 2011.

  1. tmh

    tmh

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    I just took AAMC 10 and there was a passage about hoffman vs zaitsev elimination (Passage VII, 138). I was sure I'd seen it before but couldn't find it in any previous tests. It turns out my organic book, which has some practice mcat passages in the back had used the same passage. But my book used a different answer.

    The passage shows an experiment where different leaving groups are used to compare formation of 1-hexene, (E)-2-hexene and (Z)-2-hexene.

    The table shows that the poorer the leaving group, the more likely E-2-hexene is. The AAMC answer is A) The poorer the leaving group, the higher the proportion of Hoffman Orientation. My book's answer is C) The nature of the leaving group has little effect on the orientation.

    I think my book chose C because orientation refers to stereochemistry, not which alkene is formed. Thus, the AAMC's answer would be an inappropriate use of the term.

    Anyone who took AAMC 10 want to weigh in on this?
     
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  3. MT Headed

    MT Headed snow, PBR, and bears
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    No, the table shows that the poorer the leaving group, the more likely 1-hexene is. Iodide is a great leaving group, and produces 19% 1-hexene with the first base/solvent pair. Fluoride is a terrible leaving group, and produces 70% 1-hexene with the first base/solvent pair. The results with the second base/solvent pair show a similar upward trend. The Hofmann product is 1-hexene. This is in agreement with the AAMC answer (A).

    The crux of your argument is that the phrase "Hofmann orientation" is a nonsensical trick phrase invented by the AAMC, and therefore answer (A) can be eliminated. This strategy does not lend itself to success on the MCAT.

    Easy ochem is easy. Especially MCAT ochem.
     
  4. tmh

    tmh

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    typo..

    Fair enough. I guess it would be unreasonable to use that term if it weren't real. A was the answer I put the first time, but my textbook seemed to disagree. I don't know why they would contradict the real answer.
     

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