Use the sequence rule to specify the configuration of the stereogenic center in each of the foll

Use the sequence rule to specify the configuration of the...

Key Concepts

Chirality

Chirality is a property of molecules that lack an internal plane of symmetry, making them non-superimposable on their mirror images. A chiral molecule typically contains a stereogenic (chiral) center where four different substituents are attached, leading to distinct stereoisomers known as enantiomers.

Cahn-Ingold-Prelog (CIP) Priority Rules

The CIP priority rules are a set of guidelines used to assign a priority order to the substituents attached to a stereogenic center. This ordering is based primarily on the atomic number of the directly bonded atoms, and when necessary, further points of difference in the substituent structures are considered. The rules provide a systematic way to determine the sequence in which the substituents should be analyzed for stereochemical configuration.

R/S Configuration

The R/S configuration system is a method for describing the absolute configuration of a chiral center. Once the substituents have been prioritized using the CIP rules, the spatial arrangement is examined, and the configuration is assigned based on the order in which the high-to-low priority groups are arranged relative to the observer. A configuration is designated as R (rectus, right) if the order goes clockwise, and S (sinister, left) if it goes counterclockwise.

Sequence Rule

The sequence rule involves applying the CIP priority rules to determine the order of substituents around a stereogenic center. By arranging the substituents according to their assigned priorities and then analyzing the spatial arrangement, one can assign the absolute configuration (R or S) to the center. This rule is critical in stereochemistry for accurately describing the three-dimensional structure of chiral molecules.

Transcript

00:01 I have rewritten compounds a through e, so that's a little bit easier to visualize where the stereo centers are.

00:07 In the first compound, no atom has four different things attached, no tetrahedral stereoceners.

00:16 So zero.

00:17 For the second compound, the only stereogenic center is here, where the ethoxy group is different from a methyl group, which is different from an ethyl group, which is different from a hydrogen.

00:28 Coming down here, there are no stereocentors, even though.

00:31 Though it looks like this could be, the isopropal group here is the same as the isopropal group here.

00:37 Therefore, this isn't a stereogenic center because you don't have four different things attached.

00:42 Down here, this methyl is different from a hydrogen, is different from this isobutal, is different from this long alkyl chain.

00:49 So this is a stereo center.

00:51 Same idea with this center.

00:53 A methyl is different from the secbutal, is different from this group, is different from hydrogen.

00:59 And finally, this carbon is also a stereocenter because ethyl is different from methyl, it's different from hydrogen, is different from this alkale chain.

01:08 Down here, deuterium is different from methyl is different from hydrogen.

01:13 So there's one stereo center in this compound.

01:17 Moving up to f, let's start on the left here.

01:22 A methyl group is different from an alcohol, is different from this large alkyl chain, which is different from hydrogen.

01:27 This is a stereo center.

01:29 Same for all of these centers.

01:32 All of them are stereo centers because there are four different things attached.

01:36 So, for instance, this alcohol is different from this alkyl chain, which is not the same as this alkyl chain, which is also not the same as the hydrogen.

01:43 So there's one, two, three, four, five, six stereo centers in that compound...

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