Converting Fischer Projections To Line Drawings

In this post, we will learn how to convert between Fischer, Bond-line, and Newman projections in different orders. This is an essential skill as it helps to visualize the molecule in space, and that is what a significant part of understanding organic chemistry relies on.

Let's start with the conversion between bond-line structures and Newman projections.

Converting Bond-Line Structure to a Newman Projection

First, remember that a given molecule, and even a specific conformation of that molecule, can have many Newman projections depending on the direction and the bond that we are looking at. The direction is usually given with an eye symbol or an arrow. Check the post about Newman projections if you need to refresh some of the concepts.

For example, this is how the following bond-line is transferred to a Newman when looking through the C1-C2 bond from the top-left:

I have noticed that many students struggle with this concept and after trying different approaches, I spontaneously drew a person instead of the eye for the view direction and it turns out to be a game-changer. The key helping factor here was that I was able to use the hands of the person to designate the groups pointing to the left or to the right.

Here is how it would work when using this example:

If it is not clear how this is happening, do it in the following order:

1) Determine if the Newman projection is going to have the "Y" shape or the upside-down "Y" shape.

In this case, it is going to be the "Y" shape since there are two groups pointing up and to the sides (H and Cl). We are talking about the front carbon shown in red.

2) You can now identify the groups pointing to the left or to the right. H is on the front carbon, pointing to the left, Cl is on the right. On the back carbon, we have Br on the left, and H on the right:

Converting Newman Projection to a Bond-Line Structure

In order to convert a Newman projection to the corresponding bond-line structure, you need to look at it from the side. So, first, decide the direction you are going to use. It can be any – right or left unless specified in the question.

For example, we can look at this molecule from the right side which places the Cl on the bottom-right corner and the methyl on the top-left:

After this, add the groups on the corresponding carbons pointing them towards you (wedge) and away from you (dash):

It might be helpful to convert the Newman projection to Haworth before getting the final structure in the bond-line. Haworth projection is different from the Newman in that it shows the bond between the front and back carbons. So, it is not looking directly through the bond, but rather at a slightly tilted angle:

After this, we can now project the Haworth into bond-line and place the groups according to their arrangement:

Converting Bond-Line to Fischer Projection

Here is what you need to remember about the Fischer projection:

the horizontal groups are pointing towards you
the vertical lines are pointing away from you

For example, in this molecule, the Br and H are pointing to the viewer while the two carbons connected to the central one, are pointing away from us:

Let's now forget for a moment about this Fischer projection and convert the following bond-line structure into a Fischer projection:

If you look at the molecule from the top, you will see the following representation where the twogroups on the side are pointing towards and the ones on the top and on the bottom are pointing away from you. We will show the ones on the sides with wedge lines and the others with dashed lines:

There are two wedge and two dash lines which may look strange to you since we always have one of each and then the two solid lines, but it is okay-it all depends on the direction we are looking at the molecule.

After this, you need to simply show all the bonds with plane solid lines, keeping in mind that thehorizontal groups are pointing towards you and the ones on thevertical line are pointing away from you:

How do you remember which ones are pointing towards you?

Well, you can remember that Fischer projections like you and they are coming to give you a hug with open arms:

Or, you look at the Fischer projection like you are in the gym and need to grab the molecule. In this case, as well, the horizontal groups have to be pointing towards you.

Converting Fischer Projection to Bond-Line Structure

Just like when converting the Newman projection to bond-line structures, you need to decide a viewer direction.

Let's, for example, look at the following Fischer projection from the left:

When doing so, the top group (aldehyde) is going to be the left side of the bond-line structure. Keep in mind that the horizontal lines are pointing towards you in the Fischer projection. Notice that they are also pointing to the viewer on the side which means the H and the OH are going to be wedge lines when we look at the structure from the left (this is not the final zig-zag structure yet – we are only looking at the molecule from a different direction):

Again the wedge and dash are relative to the direction we are projecting the molecule and if the viewer was on the right side, then the Cl and Br would've been wedge. The aldehyde group, however, would've been on the right side and the methyl on the left. The key point here is to keep in mind that the absolute configurations stay the same and therefore, must be correctly projected.

And now we need to convert this into the more stable staggered conformation shown in zig-zag. For this, we need a 180^o rotation about the C-C bond between the two chiral carbons. This puts the methyl group (on the rightmost) up and the OH with the Br pointing down changing their wedge and dash notation:

And this is the final answer drawn in a conventional zig-zag structure:

R and S Configuration and Conversion of Structures

Aside from these strategies for converting between different representations of organic molecules, there is more good news if you still don't quite like those!

Regardless of the molecule shown in bond-line, Newman, or Fischer projection, it is still the same molecule! And therefore, it must have the same absolute configuration of all the chiral centers.

This means, for example, when you are converting a Fischer projection to a bond-line, you can simply draw the zig-zag with the correct number of carbons and add the groups by randomly assigning them wedge and dash notation. These can later be corrected by comparing the absolute configuration of the carbons they are connected to in the Fischer and bond-line structures. Of course, they must be the same in the final structure:

An important application of Fischer projections is the ease of conveying the stereochemistry of carbohydrates and their conversion from Fischer, Haworth, and chair structures.

Converting Newman Projection to a Fischer Projection

A good strategy here is to convert the Newman projection to a bond-line structure and from there get to the Fischer projection as we did above.

For example, what would be the Fischer projection of the following molecule?

Again, if it the direction is not specified, you can choose one and draw the bond-line structure based on that.

Let's look at the molecule from the right side. This will put the CN and Br groups as wedge lines, the OH and Cl as dash lines. The zig-zag will have the methyl on the bottom-left side and the ethyl group on the right side respectively:

Now, to transform the bond-line into a Fischer projection, we can look at from the top such that the methyl group goes on the top of the Fischer projection:

Remember, to flip the bond between the carbons in order to have the horizontal groups as wedge lines before drawing out the Fischer projection:

Below are some practice problems converting between Bond-Line, Newman, and Fischer projections. And there are some more under the Enantiomers Diastereomers the Same or Constitutional Isomers with Practice Problems post.