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

Name: Problem 47, Chapter 5: Organic Chemistry
Uploaded: 2020-06-24T13:55:47-08:00
Duration: 4 min 9 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 we have two organic molecules here, and we want to go ahead and identify the chiral centers, as well as assign the configuration for each chiral center.

00:09 So looking at organic compound a here, it looks like we have two different chiral centers, and so i'll go ahead and denote one with red here, a little red dot.

00:20 So that's going to be one chiral center because it is connected to four different groups.

00:24 We're connected to our methyl group, our hydrogen, our bromo, and then the rest of the parent chain are two carbons, and as well as the bromo and hydrogen.

00:33 So we would say that is a different group.

00:37 So another chiral center is going to be this one here.

00:41 I'll go ahead and draw it in green this time, just so it'll be easier for me to refer to later.

00:47 And of course, we can say the same thing that it's connected to the four different chains as well.

00:52 And now looking at organic compound b, we see that we have a carl center right here, because it is connected to the phenyl group.

01:01 The hydrogen, the alcohol group, and the rest of the parent chain, the carbiczylic acid.

01:08 So we would say those are four different groups.

01:11 And then for this, this is another carol center here, because we are connected to our carbaclylic acid, our amine, our hydrogen, and the rest of the parent chain, which is eventually connected to the funnel group.

01:24 And so we would say that we do have four different groups there.

01:27 Okay.

01:28 And now we want to go ahead and assign configuration for each carol center.

01:31 So i'll start with the organic compound a at the red one.

01:35 So i'll assign my priorities.

01:36 Prior to number one goes to the bromo group, of course, because it is the highest weight.

01:40 And then this carbon is going to be number two, as it is connected to the bromo group.

01:46 And then this is our methyl group is going to be number three, and our hydrogen is going to be number four.

01:50 And so it looks like we are going counterclockwise, and this is going to be correct, because we do our hydrogen going away from us, which is desired.

01:58 And so we would say that that is going to be an s, right? and so now looking at the green one, we see that our bromo group's number one, just like before, and then the carbon connected to the bromo group, just like before is going to be number two, then methyl is number three, and hydrogen is number four...

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