How do I convert a newman projection to a fisher projection v.ochem

[bigDee]

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[0Complications]

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[0Complications]

I really need to understand how to do this.

How is it converted to a fisher projection?

You're right, you do need to know this. 😉

The easiest way I know how to do this is:

Basic points-

On Newman Projections the crossing point is the front carbon (in reference to you looking down the molecule) and the circle is the back carbon, so anything attached to the crossing point is attached the front carbon and anything attached to the circle is attached to the back carbon. It is assumed that the front and back carbon are connected.

Remember that in a Fischer projection the vertical axis is the C-C "backbone" and the uppermost and lowermost functional groups (We'll call them R) are drawn into the paper. The ones on the sides are drawn coming out of the paper. So with this in mind you have a Top R and Bottom R going into the paper and 4 side groups coming out of the paper.

You always call the top carbon carbon 1 (or alpha if you're oldschool) and then count down the molecule, so the second carbon down is C2 and so on.

Now to draw these bad boys-

1) Draw your Fischer projection and picture yourself laying down the molecule flat (but don't forget the direction of the projecting arms) and looking down Carbon 3 (assuming the top group is C1, so this should be the the second carbon up from the bottom).

2) Now remember the way each component is projecting, the two side bars are going to point up above you and the bottommost Carbon (or whatever it is) is going to point down below you (from the vantage point of looking down the molecule).

4) Now on the front carbon (C3 in our example), you'll notice that the D and Z side components (from your drawing) appear to be pointing up and the B is pointing down, so based on the orientation from above, you draw in the B on the bottommost point, the D on the left of C3, and the Z on the right of C3.

5) Now (there are a number of different ways to do this step and the others for that matter, but this one is pretty easy) you take the backside of the Newman projection and rotate it 180 degrees causing the molecule to be eclipsed. Now you'll see the O next to the B on the bottom and the D next to the C and the A next to the Z. This conversion is simply to make it easier to see where they fit on the molecule (you can do it in your head, but it's important to see that if you don't rotate the back back carbon by 180 degrees then your top point of the fisher projection would be as if it were pointing out of the page and the sides of the 2nd carbon would be as if they were pointing into the page, which is the opposite of how they are supposed to be. SO DON'T FORGET TO ROTATE THEM.). Now you'll see that the bottommost group on the back carbon "O" is pointing down, so put it on the topmost point of the Fischer projection. The Two side components are then C on the left and A on the right. (I added a picture to show what I'm describing, sorry for the poor drawings, paint is not so great...). Now you're done!

 

[0Complications]

Wow. That image quality is terrible. If you PM me with your email address I'll send you the full size image.

 

[Foghorn]

Make the conformer eclipsed.

 

[lumanyika]

You're right, you do need to know this. 😉

The easiest way I know how to do this is:


5) Now (there are a number of different ways to do this step and the others for that matter, but this one is pretty easy) you take the backside of the Newman projection and rotate it 180 degrees causing the molecule to be eclipsed. Now you'll see the O next to the B on the bottom and the D next to the C and the A next to the Z. This conversion is simply to make it easier to see where they fit on the molecule (you can do it in your head, but it's important to see that if you don't rotate the back back carbon by 180 degrees then your top point of the fisher projection would be as if it were pointing out of the page and the sides of the 2nd carbon would be as if they were pointing into the page, which is the opposite of how they are supposed to be. SO DON'T FORGET TO ROTATE THEM.). Now you'll see that the bottommost group on the back carbon "O" is pointing down, so put it on the topmost point of the Fischer projection. The Two side components are then C on the left and A on the right. (I added a picture to show what I'm describing, sorry for the poor drawings, paint is not so great...). Now you're done!

i think #5 sums it up perfectly IMO. great explanation OComp!