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

Name: Problem 10, Chapter 5: Organic Chemistry
Uploaded: 2020-05-14T05:31:25-08:00
Duration: 6 min 12 s
Channel: Bobby Barnes
Description: Assign R or S configuration to the chirality center in each of the following molecules:

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

Key Concepts

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.

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.

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.

Transcript

00:01 They want us to assign r or s configuration to the chiral center in each of the following molecules.

00:08 So let's go ahead and start with the one in a we have.

00:13 So in this case, so we already have hydrogen is our lowest priority group.

00:18 So there's no issues there.

00:19 It's already in the back.

00:20 So actually, let's go ahead and draw a mock one just so we can put the numbers down.

00:24 So we have four.

00:26 We have this in the front.

00:28 Like that.

00:28 All right.

00:30 Now, between a sulfur, a carbon, and a carbon, the sulfur has higher priority.

00:36 So our one is going to be facing towards us.

00:38 Then we need to decide, well, what has higher priority? so actually, let's draw this group out.

00:45 So that should be a carboxylic acid.

00:50 And then over here, we just have three hydrogens attached.

00:53 So if we do the little punchout game, notice that, well, we have a hydrogen.

00:58 And then this carbon actually has three.

01:00 Three oxygen's attached to it.

01:02 So because of that, the carbonyl cellc acid is going to take higher priority, so we'd have two there, and then we're going to have three like that.

01:10 So now all we need to do is do our rotation, since our lowest priority group is in the back.

01:16 And so we're going to rotate like this here.

01:20 So the way i like to remember this is, so when you're drawing an r, we would draw it like this.

01:26 And so notice that the curve goes like that.

01:29 So this is going to be to the right for r.

01:34 Or you just remember r is to the right.

01:36 And then for s, a lot of times, or normally, when you draw an s, you start up here, and the rotation goes like that.

01:45 S is going to be to the left.

01:48 So notice over here we're rotating to the left.

01:52 So that means this chiral center here is going to be s.

01:56 Let's go ahead and box that.

01:58 Now for b .e, let's go ahead and draw our little skeleton to start.