Assign R or S configuration to each chirality center in the following molecules:

Name: Problem 44, Chapter 5: Organic Chemistry
Uploaded: 2020-06-24T13:01:40-08:00
Duration: 5 min 25 s
Channel: Travis Maslanik
Description: Assign R or S configuration to each chirality center in the following molecules:

Assign R or S configuration to each chirality center in the...

Key Concepts

Chirality Center

A chirality center, often a carbon atom, is one that is attached to four different substituents, leading to non-superimposable mirror images (enantiomers). Recognizing a chirality center is fundamental when analyzing molecular stereochemistry and determining the molecule’s chirality, as it is the point at which the spatial arrangement of atoms can produce two distinct configurations.

Cahn-Ingold-Prelog (CIP) Priority Rules

The CIP priority rules are a systematic set of guidelines used to rank the substituents attached to a chirality center based on their atomic numbers and connectivity. These rules allow chemists to unambiguously determine the order of priority, which is essential when assigning the absolute configuration (R or S) to stereocenters.

Absolute Configuration (R/S)

Absolute configuration refers to the spatial arrangement of the substituents around a chirality center as described by the R (rectus, meaning right) or S (sinister, meaning left) designation. This systematic nomenclature is determined by orienting the molecule so that the lowest priority group is positioned away from the observer, and then evaluating the order of the remaining substituents according to the CIP rules.

Stereochemical Representations

Understanding different molecular representations, such as wedge-and-dash diagrams or Fischer projections, is crucial for visualizing three-dimensional arrangements of atoms around a chirality center. These representations help in accurately assessing the spatial orientation of substituents, which is necessary for the correct application of the CIP rules and the determination of the R or S configuration.

Transcript

00:01 So this question asks us to assign configuration for each of the chiral centers in each of the following molecules.

00:07 So looking at, we actually see that for each of one of them, we're going to have two different stereogenic centers.

00:14 And so i labeled one with a green dot and one with blue dot just to guide my discussion.

00:19 So looking at organic compound a, i'm looking at the chiral center that is designated with the green dot.

00:26 And so i'm going to go ahead and assign configuration for that one.

00:29 And so what i see here is when i designate my priority is that the oxygen, of course, is going to be priority number one.

00:36 And then we see that this carbon connected to the chloride, or the chloride group is going to be number two.

00:42 And then this carbon here connected to the rest of the chain is going to be three.

00:46 And then our hydrogen is going to be number four.

00:48 And so it looks like we are going clockwise, which we would normally say r.

00:53 However, we want our hydrogen to be going away from us, but here we see it's coming towards us.

00:58 So instead of r, it's actually going to be s.

01:02 And so i would say this group here is going to be s.

01:10 And so now looking at the blue one, i'm going to assign my priorities for that.

01:14 Carole center, and i see that the chloral group is going to be number one.

01:18 And then the carbon connected to the hydroxyl group is going to be number two.

01:25 And then the carbon connected to the rest of the chain.

01:27 It's going to be number three.

01:29 And then the hydrogens number four.

01:31 And so what i see here is that, i'm going counterclockwise, and so i would say that this is s, and i will, in fact, have s because the hydrogen is going away from us.

01:43 So i can go ahead and write that here, and that this carous center is s.

01:48 Okay, and now looking at b, i'm going to go ahead and look at the green chiral center, and what i see here is that our priority number one is going to be this particular carbon here, because if we go ahead and look at what we're, well, this one's a little bit tricky, so let's actually take a step back here.

02:12 And we go ahead and compare the next carbons.

02:16 So that would be this one, this one, and this one, and we see that they're all ch2, right? and so we're going to have to go to the next carbon.

02:24 And so that would be this one, which we see is connected to two carbons and one hydrogen.

02:32 And then we see that this one here is connected to one carbon and two hydrogens, whereas this carbon here is connected to three hydrogens, right? and so we can designate priority based on that, right? so i'm going to take all those dots away.

02:50 And so what we see here is that this, what we saw is that this is the highest priority because eventually it's going to be connected to mark carbons.

02:58 And then this is the second highest priority.

03:00 And then this is the third priority because it's eventually going to be connected to just three hydrogens...

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