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3D drawing. Urgent

  1. Oct 22, 2011 #1
    We have hit stereochemistry , and I realize I will be screwed unless I can get my drawings down-pat. Okay, so, let's say the question is:

    Draw clearly structures for the pair of enantiomers of each:

    a) 3-bromo-1-butanol

    To start, I drew out the stick-diagram, and identified the stereogenic center. I then realized that I'd have to make a proper 3D representation of it to clearly show the structure in relation to its enantiomer. I hit a road block. At the stereogenic center, you'll have two bonds in the plain of the paper, one going away (dashed) and one towards (wedged).

    My question is: How are you to distinguish which gets which type of line? The only hint I have in my head is that you'd give the dashed line to lowest priority at the center (in this case, hydrogen). But, how would you determine if the bromine, say, gets a solid line or a wedged line?

    Here's an image of my professors answer:
    http://i1120.photobucket.com/albums/l485/Marconis/Picture1.png

    He represented the Br with a solid line...why? Why couldn't it be drawn with a wedged line, and be in the place where the methyl group is? If I didn't draw it like that, would my enantiomers be completely false? Please, explain clearly...I'm perishing over here.

    Thank you so much in advance.
     
  2. jcsd
  3. Oct 22, 2011 #2

    Borek

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    Staff: Mentor

    You can select any two bonds to be on the plane, it doesn't matter which ones you selected - as long as you are consistent and draw the other enantiomer the same way.
     
  4. Oct 22, 2011 #3
    That's what I was hoping for, it just gets confusing when you draw something one way and then the answer key shows something totally different. I know that in stereochemistry, compounds are very sensitive in how they are to be drawn or else you can totally mess it up, so I wanted to be sure this wasn't the case here. Thank you!
     
  5. Oct 22, 2011 #4

    Borek

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    Staff: Mentor

    I can only sympathize, but as you will get experience you will see when they are the same. It is just a matter of time.
     
  6. Oct 22, 2011 #5
    Could you perhaps help me with the following? It's not so much a homework question as it is general guidance, so I apologize if I am asking in the wrong forum.

    I am having trouble converting Fisher projections into Newman projections, and vice versa. I have gotten several correct, but the method I am using has failed me on others so I think I am doing it incorrectly. Any advice on the following is greatly appreciated:

    For (b), the question tells you do draw a correct Newman Projection that correctly shows the stereogenic centers. I am so confused on how to do this:

    http://i1120.photobucket.com/albums/l485/Marconis/Picture1-1.png

    So it pretty much wants me to finish up the Newman with correct placements of atoms.

    The same goes for this:
    http://i1120.photobucket.com/albums/l485/Marconis/Picture2.png

    Thanks in advance.
     
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