Fischer Projections - Online Tutor, Practice Problems & Exam Prep

Fischer projections are 2D representations of chiral molecules, where chiral centers are indicated by the intersection of lines. In these projections, aldehyde and ketone groups are positioned at the top. The stereochemistry is simplified by removing wedged and dashed bonds, focusing on the arrangement of four different groups attached to a chiral carbon. Understanding Fischer projections is essential for visualizing carbohydrates and their configurations, aiding in the study of stereochemistry and molecular interactions.

Fischer Projections Concept 1

Hey, everyone. So in this video, we're going to talk about Fischer projections. Now they themselves are 2D representations of chiral molecules where chiral centers are symbolized by the intersection of two lines. And here we're going to have solid wedges, so these solid wedges here are for our horizontal lines, the lines on the sides. And then here we're going to have our dashed wedges or lines, so these are dashed. These are for our vertical lines. Here we can transform this representation into a Fischer projection. So what we do here is we would not show the carbon, and we would show that carbon which is chiral being connected to those same groups. Now, remember, a chiral carbon or chiral center is when carbon is connected to four different groups. So we have x, y, z, and w here. These are representative of four different structures. Alright. So then we're going to write them in. So this would be y up here, z here, oh, man. x here. z here and w over here. So we've just created our Fischer projection. And the carbon is still here, it's just invisible. It's still chiral, so I'm putting an asterisk next to it to represent that it's still a chiral center. Alright. So just remember, here we have the showing of our chiral carbon with wedged and dashed bonds, and we've just converted it into a Fischer projection, where we have eliminated the stereochemistry and made it 2D. So the lines themselves no longer have wedged or dashed representations.

Fischer Projections Concept 2

When drawing Fischer projections, aldehyde and ketone groups are always represented on top. If we take a look here at this illustration, we start out with our bond line form. Don't worry, you're not going to have to convert from the bond line form to the wedge dash form. So, I'm just showing you that this here can be restructured to give us this form here. And it's in this form here that's important for you to know how to go from it to your Fischer projection. Now remember, your Fischer projection is a 2D representation, so we will not have stereochemistry. That means we would eliminate these dashed bonds and these wedged bonds when drawing it. Now, here we have this, this, and this as our chiral centers in terms of this, carbohydrate. And so, this carbon here, we illustrate it as this carbon here. This carbon here would be this carbon here. And this carbon here would be this carbon here. We already have our aldehyde here, and we already have our CH₂OH group here on the bottom. All we have to do now is just add what's connected to these 3 chiral carbons. We have an H and an OH, HOH, and then HOH again. So we've gone from the wedge dash form to our Fischer projection form, which again is just a 2D representation. Remove the stereochemical bonds, no wedge bonds, no dash bonds to give us our Fischer projection at the end.

Fischer Projections Example 1

Here it says, convert the wedge dash structure to a Fischer projection. Remember, a Fischer projection is a 2D representation of our monosaccharide unit here. So, that means we need to eliminate all our wedged and dashed bonds. So here we'd have still our CH₂OH which we show. Here we do not show the carbon but it's double bonded to the oxygen. And we have our 2 chiral carbons. Each one would still be connected to an OH and an H respectively. And then finally, we wrap it up with a CH₂OH here on the bottom. So this would represent our Fischer projection where we've converted our wedge dash structure to it. Again, it's a 2D representation. You need to eliminate your wedged and dashed bonds.

Here’s what students ask on this topic:

What is a Fischer projection in organic chemistry?

A Fischer projection is a 2D representation of a chiral molecule used in organic chemistry. It simplifies the 3D structure by depicting chiral centers as the intersection of horizontal and vertical lines. The horizontal lines represent bonds coming out of the plane (towards the viewer), while the vertical lines represent bonds going into the plane (away from the viewer). This method is particularly useful for visualizing carbohydrates and their stereochemistry, as it eliminates the need for wedged and dashed bonds, focusing instead on the arrangement of four different groups attached to a chiral carbon.

How do you convert a 3D structure to a Fischer projection?

To convert a 3D structure to a Fischer projection, follow these steps: First, identify the chiral centers in the molecule. Next, orient the molecule so that the horizontal bonds (coming out of the plane) and vertical bonds (going into the plane) are clear. Then, draw the chiral centers as intersections of horizontal and vertical lines. Place the aldehyde or ketone group at the top and the CH₂OH group at the bottom if applicable. Finally, add the substituents to the chiral centers, ensuring that horizontal lines represent bonds coming out of the plane and vertical lines represent bonds going into the plane.

Why are Fischer projections important in studying carbohydrates?

Fischer projections are crucial in studying carbohydrates because they provide a simplified 2D representation of complex 3D structures. This simplification helps in visualizing the stereochemistry and configuration of carbohydrates, which is essential for understanding their chemical behavior and interactions. By eliminating the need for wedged and dashed bonds, Fischer projections make it easier to compare different carbohydrate molecules and identify isomers, aiding in the study of biochemical pathways and molecular interactions.

What is the significance of the horizontal and vertical lines in a Fischer projection?

In a Fischer projection, the horizontal and vertical lines have specific meanings. The horizontal lines represent bonds that come out of the plane of the paper towards the viewer, while the vertical lines represent bonds that go into the plane of the paper away from the viewer. This convention helps in visualizing the 3D arrangement of atoms around a chiral center in a simplified 2D format. Understanding this distinction is crucial for interpreting the stereochemistry of the molecule accurately.

How do you identify chiral centers in a Fischer projection?

To identify chiral centers in a Fischer projection, look for carbon atoms that are connected to four different groups. These intersections of horizontal and vertical lines represent the chiral centers. Each chiral center will have four distinct substituents, which can include hydrogen, hydroxyl groups, alkyl groups, or other functional groups. Identifying these centers is essential for understanding the molecule's stereochemistry and for converting between different representations of the molecule.