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Newman projection que.

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UndergradGuy7

Full Member
10+ Year Member
Jun 24, 2007
897
2
  1. Pre-Dental
    Well, I haven't started reviewing Organic Chem, but I know that a metal catalyzed hydrogenation is a syn-addition. Since it adds to the same side of the double bond I thought B would be the answer.

    C. is more stable since the CH3 are trans to each other making it more stable and the D are also trans. While in B only the CH3 is trans, but not the D.

    So, I dno?
     

    UCB05

    Full Member
    Jun 14, 2009
    800
    3
    1. Pre-Dental
      since you're now differentiating between H and D, the orientation of the bonds matter. You initially start out with cis-2-butene. Addition of D2 over metal catalyst adds these D's in a syn fashion. This leads to a specific orientation where, looking down the C2-C3 bond, the -C(1)H3 and -C(4)H3 are eclipsed, and the two new D's are eclipsed. This is not one of the answer choices, so you also have to take into account the fact that the C2-C3 bond can now freely rotate. You have to keep the same bond orientation, but if you rotate about C2-C3, you can get the answer shown in C. The incorrect answer given in B can be arrived at if the D's added in anti fashion.

      [URL=http://img28.imageshack.us/i/scand.jpg/]
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      kpanesar

      Full Member
      10+ Year Member
      Dec 22, 2009
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      0
        i just drew it out... so you have your cis-2-butene and after reduction i had the dueterium coming out at my on C2 and C3 and the C1 and C4 going away and then the hydrogen pointing down.

        so for newman's i just start by drawing C2 so if you're looking at the propellor then the methyl is at 10 o clock, the dueterium at 2 o clock and the hydrogen at 6 o clock. then you just rotate bond btw C2-C3 so that the substituents are on opposite sides (which is the case because rotating 180 ends up with the deuterium now going away from you and the methyl coming towards you.
         

        RSD2014

        Full Member
        Sep 2, 2009
        202
        0
        1. Pre-Dental
          Hey everyone.. I'm having trouble with this question. Answer choice B looks more like cis to me than does C. How do you approach this problem?

          http://img38.imageshack.us/img38/8246/18280336.png


          First draw Cis-2-butene and reduce it with D2 (Syn-Addition).
          In converting a perspective drawing of a molecule into Newman projection, we keep the top section, and rotate the bottom section. Looking at C2, we have CH3 at Top, D at Left, H at Right. We rotate C3 180 degree, CH3 at Bottom, D at Right, H at Left. Which is Answer C.
           
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