A) Identify the chirality centers in the molecule.

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Question

A) Identify the chirality centers in the molecule.

B) Determine the configuration of each chirality center.

Chemical structure of a molecule for identifying chirality centers in biochemistry.

Accepted Answer

Alright. So here's a 2 part practice problem that's broken up into part a up above, and part b down below. And part a is asking us to identify the chirality centers in the molecule that's over here on the far right. And so again, if you guys don't remember how to determine the configuration of a chirality center from your old organic chemistry courses, then make sure you guys rewatch these videos that I'm linking you to in the comments section down below. And so, recall from our previous lesson videos that a chirality center is literally just a carbon atom. It's a special carbon atom. It's a carbon atom that is chemically bonded to 4 distinct chemical groups or 4 distinct chemical pathways. And so, essentially, what we can see is this first carbon atom in our molecule, notice that it is double bonded to a single chemical group of an oxygen atom. And so we have 2 pathways, 2 bonds, so this bond here and this bond over here, that are leading to the same chemical group. So we don't have 4 distinct chemical groups attached to this carbon atom. And for that reason, this carbon atom right here is not a chirality center, and we don't need to worry about its configuration. Now, the same applies for this carbon atom over here on the far right because we know that even though they're not shown, these carbon atoms are bonded to 4, 4 groups. And so essentially, we know that there's going to be a hydrogen atom on a dash, as well as another hydrogen atom on a wedge. And so essentially because this, path right here and this path right here are leading to the same exact chemical group of a hydrogen atom, that means that there are not 4 distinct chemical groups attached to this carbon atom right here. And so this carbon atom is not a chirality center, and we don't need to worry about its configuration. Now, when we look at this carbon atom on the other hand, notice that again, it has 4 distinct chemical groups. And so we know that there's going to be a hydrogen on a dash going down here, and we know that because, the hydroxyl group is on a wedge, so the hydrogen must be going on a dash. And no matter which chemical, path that you look at, if you look at this path here, this path this way, or this path going this way, or this path going down, all 4 pathways have a distinct chemical group or a different chemical group. And so, for that reason, we can actually say that this carbon atom right here is a chirality center. And, the same applies for this carbon atom over here as well. So, no matter which chemical path that you take, we know that there's gonna be a hydrogen atom coming up on a wedge here, because we have the hydroxyl group on a dash. And so essentially, no matter which chemical path that you take, whether you take this path this way, this one going down this way, this one going this way, or this one going up, that all 4 chemical groups are chemically distinct. And so that means that this carbon atom here, shown here, is also a, chirality center. And so what that means is we have 2 chirality centers in this molecule. These two carbon atoms that are shown, and we've identified the chirality centers in this molecule. So part a is complete. Now, moving on to part b, it says to determine the configuration of each chirality center. And so, again, if you don't remember how to determine the configuration of a chirality center, make sure that you watch the videos that I'm linking you to in the comment section below. But, over here in this box, we have a little refresher to help you guys refresh the basics. And And so we know that there are 2 configurations that a chirality center can possibly have, an r configuration or an s configuration. And so the r configuration is where the clockwise orientation of priorities number 123 are, going to be in a clockwise orientation. And then s configuration is when the orientation of priorities 123 is in a counterclockwise orientation. And so, what something that we need to keep in mind, is that, if the 4th priority is not on a dash, then we actually need to flip the configuration that it looks like. And so the 4th priority is going to be really important, as well to keep in mind. And remember that the way that we determine priorities is by comparing the atomic numbers of the atoms that are connected to each of these carbon atoms. And so, if we take a look at these 2 chirality centers, we're first gonna look at this chirality center here and determine its configuration. And so, looking at this pathway going here, notice that the first atom that's attached is an oxygen atom. Going in this pathway this way, the first atom is a carbon atom that's attached. And also going this way, the first atom is a carbon atom. And going this way, the first atom is a hydrogen atom. And so, by comparing these atoms here that are in red, the 2 carbons, the hydrogen and the oxygen, we're gonna be comparing the atomic numbers. And so, notice that of these 4 atoms, oxygen has the highest atomic number. And so that means that the path that's leading to the oxygen is gonna have the highest priority, priority number 1. So we can put a one here to remind us that this pathway here is priority number 1 for this chirality center. Now, going to the right and to the left, we know that we have 2 carbon atoms over here, and, those 2 have a higher priority than the hydrogen, since the hydrogen is atomic number of 1, so it has the lowest priority. And so essentially, what we can say is that this hydrogen is gonna be priority number 4. So now what we need to do is determine which of these two pathways is actually going to have a higher priority. Which one's gonna get priority 2, and which one's gonna get priority 3? And so, in order to determine that, what we need to do is compare the atoms in each of the paths. So what we're gonna say is the path going to the left will be path number 1 over here, and then the path going to the right is gonna be path number 2. And so, essentially, what we'll see is that both of these paths initially lead to a carbon atom that's directly connected. And so, from that point, what we need to do is look at the constituents of these carbon atoms. And so the constituents are just the chemical groups that are bonded to those carbon atoms. And so notice for this carbon atom over here, which is this carbon atom right here, it leads to 2, it has two paths leading to an oxygen atom. And so, what that means is we can put an oxygen atom twice, and then also going this way, we have a hydrogen atom that's attached. So those are the constituents of this carbon atom here. Now we need to do the same for this carbon atom over here, which is this carbon carbon atom right here. So going up, notice that the first atom is an oxygen atom, so we can put an oxygen right here. And then going down this way, the first atom is a carbon atom, so we can put this carbon atom over here. And then going up this way, the first atom is a hydrogen atom. And so now that we have the constituents, we can, do a playoff type system where we compare each of the atoms, and compare the atomic numbers to determine which path is gonna get a higher priority. So comparing these two atoms right here, they have the same atom of a carbon, so they have the same atomic number, and there's a tie here, between both paths. And the same applies for these these 2 atoms, these 2 oxygen atoms. But looking at the oxygen and the carbon atom, notice that oxygen atom has a higher atomic number than the carbon atom. And so what that means is that path number 1 here is the winner, and it's going to have a higher priority than path number 2. And so, remember, path number 1 is this red path that's going this way right here. And so what that means is we can label it as being priority number 3. I'm sorry, priority number 2, because it has a higher priority than this blue path, which is going to be priority number 3. And so now that we've determined the priorities for all 4 chemical groups on this chirality center, we now can draw arrows from priority 1 to priority 2, priority 2 to priority 3, and priority 3 back to priority number 1, skipping priority number 4. And so, notice that the orientation of priorities 1, 2, and 3 is a clockwise orientation where it goes from 1 to 2, 2 to 3, and 3 back to 1 in a clockwise fashion. And a clockwise orientation is suggesting an r configuration for this chirality center here. Now, remember that we always need to take into account the 4th priority. And so if the 4th priority is not on a dash, then we need to flip the configuration that it looks like. But looking at our 4th priority here of this hydrogen, notice that it is on a dash. So we don't have to worry about flipping the configuration, and the configuration is going to be exactly what it looks like, which is an R configuration with a clockwise orientation of priorities 123. So we can label this chirality center right here as being an R configuration. And for our answer over here, we can put an r. And so really that is it for the configuration of this chirality center. Now, remember that our molecule has 2 chirality centers, and we only determine the configuration of this one. So we need to repeat this process on this chirality center, which is this carbon atom over here. So what we can do is get rid of these arrows over here so that we can repeat this same process on this carbon atom right here. And so, essentially, what we'll see is that this oxygen atom going up is gonna have a higher priority than either of these, other atoms that are connected to the other pathways. And so what that means is that this, pathway going up is gonna have priority number 1. And so we can put priority number 1 next to this hydroxyl group. And then, again, our hydrogen atom going this way is gonna have the lowest priority of priority number 4. So then, all we need to do is determine which of the these pathways, this pathway or this pathway here, is gonna get a higher priority of priority 2, and which one's gonna get priority 3. And so, comparing, we'll say that this pathway going to the left will be path number 1 here, and then, this pathway going to the right here will be path number 2. And so, notice that both atoms of, these paths are gonna be a carbon atom. So we can put a carbon atom there. And then, what we need to do is look at the constituents of these carbon atoms or the chemical groups bonded to those carbon atoms. And so essentially, notice that this carbon atom over here, which is this carbon atom right here, is bonded to an oxygen atom directly, so over here we can put an oxygen atom. And it's also bonded to a carbon atom going this way, so we can put a carbon atom over there. And it's also bonded to a hydrogen atom, so we can put a hydrogen atom down here as well. Now looking at path number 2, notice that it is bond, so essentially this carbon atom right here, notice that it is bonded to a oxygen atom going this way, so we can put an oxygen an oxygen atom here. And then it's bonded to 2 hydrogen atoms, so we can put hydrogen down here. So we have oxygen here and, 2 hydrogens right here. And so now that we have our atoms, what we can do is do our direct comparison. And so the carbon with the carbon here is, the same atomic number, so there's a tie between these two paths. The oxygen and the oxygen, again, there's a tie between these two paths. And then, the carbon with the hydrogen right here, notice that the carbon atom has a higher atomic number than the hydrogen. So what that means is that path number 1 here is going to be the winner, and it's gonna have a higher priority than path number 2. And path number 1, again, is this red path that's shown right here. So what that means is we can show this, red path, going this way, as being priority number 2. And then, of course, that means that this other path over here will be priority 3. And so now that we've assigned priorities to all chemical groups of this chirality center, we can draw arrows from 1 to 2, 2 to 3, and 3 back to 1 skipping priority number 4. And so looking at this, notice that our, the orientation of our priorities looks like a counterclockwise orientation. And a counterclockwise orientation of priorities 123 suggest an s configuration. So this might be tempting to put as an s configuration. However, we cannot forget that we always have to consider the 4th priority. And if the 4th priority is not on a dash, then we have to flip the configuration that it looks like. And so even though this looks like an s configuration because it's going counter clockwise, notice that our 4th priority of this hydrogen here is not on a dash. And so that means that we need to flip the configuration that it looks like. And so even though this looks like an s configuration counterclockwise, it's actually going to be an r configuration. And so, what that means is over here we can put r. And so essentially, what we've determined is that our priorities are chirality centers, So both of these chirality centers, this one right here and this one right here, both have an r configuration. And that concludes this practice problem, so I'll see you guys in our next video.

Struggling with Biochemistry?

A) Identify the chirality centers in the molecule.

B) Determine the configuration of each chirality center.

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Organic Chemistry practice set

Struggling with Biochemistry?

A) Identify the chirality centers in the molecule.B) Determine the configuration of each chirality center.

Watch next

Organic Chemistry practice set

A) Identify the chirality centers in the molecule.

B) Determine the configuration of each chirality center.