newman projection

joonkimdds

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  1. Pre-Dental
    123.jpg

    choose the true statment.
    a) this is meso
    b) this is (2S, 3S).
    c) this is chiral
    d) specific rotation is above 0 degree.
    e) this is (2R,3R).

    I think the answer key says A but I am not sure about this.

    if this is meso, can someone teach me how to draw newman projection like this in a plane sheet of paper so I can tell whether it has internal symmetery or has S or R orientation?
    I have tried many times and not sure which one is correct way of drawing among
    ......Br
    ...H-C-CH3
    CH3-C-H
    .......Br

    and
    ......Br
    CH3-C-H
    CH3-C-H
    .......Br

    and
    ......CH3
    ...H-C-Br
    CH3-C-H
    .......Br

    and so on.
     

    sajjy

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    Sep 25, 2007
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    1. Dental Student
      123.jpg

      choose the true statment.
      a) this is meso
      b) this is (2S, 3S).
      c) this is chiral
      d) specific rotation is above 0 degree.
      e) this is (2R,3R).

      I think the answer key says A but I am not sure about this.

      if this is meso, can someone teach me how to draw newman projection like this in a plane sheet of paper so I can tell whether it has internal symmetery or has S or R orientation?
      I have tried many times and not sure which one is correct way of drawing among
      ......Br
      ...H-C-CH3
      CH3-C-H
      .......Br

      and
      ......Br
      CH3-C-H
      CH3-C-H
      .......Br

      and
      ......CH3
      ...H-C-Br
      CH3-C-H
      .......Br

      and so on.

      alright...i will try to explain this 3D stuff here.....this is what i follow...
      i always use fischer projection and it makes it clear....try to follow these steps-:
      Keep the carbons in the straight line of the fischer projection
      which means that both terminal carbon (methyl in this case) will be going away from you in the fischer projection
      in Newmann projection, rotate the c-c bond so that both methyl group are towards the bottom side in eclipsed position.
      when you will draw the newmann projection with methyl on bottom sides, both Br will come on one side, and in this case on the left side....
      if you try to make fischer projection of this newmann projection, then u will have
      ......CH3
      Br---C---H
      Br---C---H
      .......CH3
      here both methyl are going away from you while Br and H coming towards you.....
      try to visualize this fischer projection and compare it with Newmann projection

      And it has a plane of symmetry or do the mirror test and this will be a meso compound.
      Hope that helps
       

      dontwakeme

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      Dec 26, 2006
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      1. Post Doc
        123.jpg

        choose the true statment.
        a) this is meso
        b) this is (2S, 3S).
        c) this is chiral
        d) specific rotation is above 0 degree.
        e) this is (2R,3R).

        I think the answer key says A but I am not sure about this.

        if this is meso, can someone teach me how to draw newman projection like this in a plane sheet of paper so I can tell whether it has internal symmetery or has S or R orientation?
        I have tried many times and not sure which one is correct way of drawing among
        ......Br
        ...H-C-CH3
        CH3-C-H
        .......Br

        and
        ......Br
        CH3-C-H
        CH3-C-H
        .......Br

        and
        ......CH3
        ...H-C-Br
        CH3-C-H
        .......Br

        and so on.


        meso.png


        2 chiral centers, same substituents, opposite stereochem. config = Meso
         

        joonkimdds

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        1. Pre-Dental
          wow...LOL.
          Thanks you guys so much for hard work!
          I guess the main reason I got confused is that they are staggered and anti so I thought that they should be something like
          ......Br
          ...H-C-CH3
          CH3-C-H
          .......Br
          so that CH3 and another CH3 look like anti and 180 degree apart (even though it should be 60 degree in fischer projection).

          Anyway everything is clear now. Thanks again.
           
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          rose786

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          Apr 25, 2006
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            The ones on the same side of the newman projection are on wedge. The ones on the other side are on dash. You can reverse it, doesn't really matter. The Bromine positions are on stick.. This configuration matches the newman because the CH3's are anti, the H's are anti, and the Br's are anti.

            Ok cool. I had to draw out it out to see what you meant.
             
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