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Orgo Questions..

Discussion in 'MCAT Discussions' started by xoomn, Aug 13, 2002.

  1. xoomn

    10+ Year Member

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    I am a bit confused on this terms...So I need help in disting. them..

    Are structural isomers = constitutional isomoers?
    Geometric isomers = could be diastereomers?
    Stereoisomer = Configurational isomers?

    What the heck is regioisomer? ;)

    Also, what would you get when Carboxylic Acid undergoes a Grignard rxn?
     
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  3. freakazoid

    freakazoid Guy Friend Extraordinaire
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    Are structural isomers = constitutional isomoers? YES
    Geometric isomers = could be diastereomers? YES

    In this distinction however, keep in mind that these two terms are like overlapping circles. The place they overlap is where the geometric isomers differ in orientation of substituents around a ring. The place where it's strictly a geometric isomer is when they differ across a double bond, since there are no chiral centers. Everything else w/ chiral centers are diastereomers.

    Stereoisomer = Configurational isomers? Um, not sure. Sounds good though.

    What the heck is regioisomer? I'm taking a wild guess here, but I would think that it was two molecules may not necessarily have the same connectivity but have two regions that are identical

    Also, what would you get when Carboxylic Acid undergoes a Grignard rxn?

    Couldn't find this reaction, so I don't think it'll be tested. However, RMgBr + CO2 --> RCOO-+MgBr
     
  4. xoomn

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    Thanks freakazoid... Here is another question that I did not get in PR Test B.

    --Reduction of 4-tert-butyl-cyclohexanone with LiAlH4 would result in what?

    A. most R, some S
    B. most S, some R
    C. Meso
    D. Achiral

    Answer was D but I don't get it. How come, I thought it would be a meso compound since it could be bisect right through the middle.
     
  5. Doctor Octopus

    Doctor Octopus Hospitalist
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    It's achiral because there are no chiral centers. The two sides of the ring are identical with respect to the carbon with the hydroxyl group attached.
     
  6. wgu

    wgu Senior Member
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    test
     

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  7. wgu

    wgu Senior Member
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    what the man is trying to say is...
     

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  8. wgu

    wgu Senior Member
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    i take that back, you get cis/trans...

    i think the rules for oppositely substituted (diff substituent) even-sized rings are
    1) optically inactive
    2) achiral
    3) diastereomers (yes, and they are still achiral)
    4) labelled cis/trans
     

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  9. Mudd

    Mudd Charlatan & Trouble Maker
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    A Grignard reagent will deprotonate a carboxylic acid and in doing so, be destroyed. The basicity of aGrignard is substantial, which is why the reation is carried out in an aprotic solvent.

    Stereiosomers are broken into configurational isomers and conformational isoemrs. Configurational isomers include optical isomers (R and S for instance) and geometrical isomers (E and Z for instance). Conformational isomers include different chair conformations.

    A regioisomer is also known as a positional isomer (both a subgroup of structural isomers), where the functional groups are the same, but the positon of the funtional group is different.

    wgu has shown an excellent example of non-superimposible geometrical isomers that are not mirror images.
     

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