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R S Configuration Assigning Priorities

  1. May 28, 2012 #1
    The Order of priority of few elements is given Below

    OCOCH3 > NH2 > COOCH3 > COOH > COCH3 > C6H6

    Can any one explain me how these priority were assigned.

    If we consider C6H6 ....out of the 6 Carbon Atoms which one should i choose ... and if i choose any one of the Six then i should add their Atomic Numbers of the neighbouring elements and then find out the Largest and that would have the highest Priority. I tried this method with all the atoms but couldnt understand .What approach should i take.

    Please Explain me atleast 3 of the above mentioned compounds so that i can get an idea of how to go about it.
     
  2. jcsd
  3. May 28, 2012 #2

    chemisttree

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    I think the C6H6 is an error and should actually be -C6H5... that is if you are determining the priority of an attached benzene group.
     
  4. May 28, 2012 #3
    Yes it is C6H5

    Sorry for the Error
     
  5. May 29, 2012 #4

    chemisttree

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    Well, that answers the following.
    When assigning priorities, you count double bonds the same way you do for alkanes. So for benzene you would consider the attached group as a carbon attached to three other carbons in the same way that a tertiary carbon of an alkane is attached to three other carbons. If you were to rank benzene against t-butyl, you would choose benzene as higher ranking than t-butyl because the methyl groups of t-butyl are of lower rank (carbon attached to three hydrogens) than the adjacent carbons in the benzene ring (carbon attached to one hydrogen and two carbons).
     
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