What is the configuration of each of the asymmetric centers in...

Question

What is the configuration of each of the asymmetric centers in the Fischer projection of

a. D-glucose?

Accepted Answer

Hey, everyone, let's do this problem and says, determine the absolute configuration of each of the Cairo centers in the following structure and were given the Fischer projection of D Talos. So to find the configuration of the Carvel centers, we need to follow the con tingled pre log nomenclature rules. And let's tailor those rules specifically for Fischer projections when we review them. So in a Fischer projection, a cardinal center is going to have four different groups, right? So the first step is assigning priorities To those four different groups. And how do we assign the priorities by atomic mass? So the higher the atomic mass, the higher the priority and we're looking at the atom that is directly connected to that Cairo center. Okay. So after we assign priorities, oh, there are a few things, a few other details for assigning priorities. So what if there is a tie between those immediate atoms that are connected to the Cairo center? Well, then we simply look at their adjacent atoms and apply the same priority rules. And another important note to make is that a double bond will count as two atoms connected to that Cairo center. A triple bond will count as three. So for example, if we have a carbon double bonded to an oxygen, that will count as if carbon has two oxygen atoms connected to it. All right. So now we've assigned our priorities were getting close to assigning R and S configuration, but it depends on the orientation of the lowest priority group. So in terms of Fischer projections, if group number four is horizontal, That will have a different criteria than if group # four is vertical. And it's actually the same criteria as wedge and dash because horizontal, those groups are wedge and vertical groups are dashed. So to determine RNS configuration, We connect groups 1 2 and three That we've assigned priorities 1 2 and three. If those groups connect counterclockwise in a circle, that'll be different than if they connect clockwise. So connecting groups 12 and three, when group number four is horizontal, if that circle is counterclockwise, it'll be our configuration clockwise will be as configuration. And the opposite is true for when group number four is vertical, counterclockwise will be s clockwise will be our in official projection. You're usually going to see group number four horizontal. So I'll just highlight that in yellow because that's probably what we will be using here. So let's see which carbons are Cairo in our Fischer projection. So it looks like all of our four intersections of carbons are Kyrill. So let's use alternating colors and determine the centers the configuration for those four Cairo centers. So I'll start with blue. So we assign our four groups of their priority are alcohol group is going to be highest priority. Hydrogen always fourth priority. Then we have two carbons. So attached to those carbons, we have oxygen, oxygen hydrogen, right? This is an elder Hyde group. So that's carbon double bonded to oxygen. So oxygen oxygen hydrogen or oxygen carbon hydrogen, well, that oxygen oxygen is going to be higher priority. And then the south part of this chain will be third priority. So group four is horizontal connecting groups 12 and three, that's going clockwise. So this will be as configuration. Alright, so I think any carbon that has the same orientation of the horizontal groups is going to be S configuration. And if they switch, then that'll switch the configuration. So we should have S S S R. So let's see if that is true. Our alcohol group highest priority hydrogen, fourth priority. Now, for all of these intersections, we're still going to have the highest priority group of the chain on top lowest priority or third priority on the bottom. So let's see if that's true. So we have two carbons connected on either side. So the top carbon has oxygen, carbon, hydrogen, bottom carbon has oxygen, hydrogen carbon. Okay, then we keep going look at the next atom, we have oxygen, carbon, hydrogen and oxygen, oxygen hydrogen. So we see that Aldo hide is still going to take priority. So we can safely apply that to the rest of the carbons connecting groups 12 and three that goes clockwise. Fourth priority group is horizontal. So that is indeed s so our next group, our next hydrocarbon is also going to be S we have alcohol. Highest priority hydrogen, lowest priority. North part of the chain is second priority. South part of the chain is third priority 12 and three is clockwise. That is s configuration. So here's where it'll probably switch right. Hydrogen, lowest priority alcohol, highest priority. North part of the chain is second priority. South part of the chain is third priority connecting groups 12 and three. This is counterclockwise and our fourth priority group is still horizontal. So that counterclockwise means we have our. So to summarize all of this in a neater drawing. Let me redraw D Talos here on the left side, we have alcohol group, alcohol group, alcohol group hydrogen. On the right side, we have hydrogen, hydrogen, hydrogen alcohol. For those intersecting carbons in our orientation from top to bottom of those cargo centers is S S S R and we denote archival centers with the asterisk. So that makes a the correct answer choice for this problem. That's it for this one. I hope this video is helpful and thank you for watching.

What is the configuration of each of the asymmetric centers in the Fischer projection of
a. D-glucose?

Key Concepts

Fischer Projections

Chirality and Asymmetric Centers

D and L Configuration

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