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help with simple orgo question

Discussion in 'MCAT Discussions' started by ankit1ag, Apr 9, 2007.

  1. ankit1ag

    2+ Year Member

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    Can someone help me with this question:

    -how is C-5 a chiral carbon. It is not bonded to four diff subst. because of the 4 & 6 CH2 groups. And tell me why 2 & 7 are not chiral. Is it because they are only bonded to 3 subst.?

    Carvone is shown below with certain carbon atoms labeled.


    [​IMG]

    (+)-Carvone and (–)-carvone differ in the orientations of the substituents around which of the following carbon atoms?


    A) Carbon 2 only
    B) Carbon 5 only
    Ex:Carbon 5 is the only stereogenic carbon atom (chirality center); carbons 2 and 7 are not stereocenters. Thus, answer choice B is the best answer.


    C) Carbons 2 and 5 only
    C) Carbons 2, 5, and 7 only
     
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  3. HippocratesX

    HippocratesX Member
    7+ Year Member

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    Since it is a ring structure, you have to treat each side of the carbon that you are looking at like a substituent...so even though there are 2 CH2 groups, like you said, if you continute following the molecule on each side, they are different. The right side of carvone has a carbonyl group (C=O) and the left side does not, so that makes them 2 different substituents, which makes the carbon chiral. If this were NOT a ring structure and it was linear, then you are right, it would not be a chiral molecule.

    so one of the substituents on the right side would be CH2-C=O and the other side would be CH2-CH-CH3. ANd the other 2 substituents for this chiral carbon would be a Hydrogen which is not shown, and the C-CH2-CH3 group hanging below.
     

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