Chiral centers

[deleted647690]

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I always thought that the number of stereoisomers for a compound could be calculated from 2^n, where n was the number of chiral centers.

I was taught that a chiral center was a carbon with 4 unique substituents, but according to this website, carbons with only 3 unique substituents are included?

Illustrated Glossary of Organic Chemistry - Stereocenter (chiral center)

Is this wrong?

 

[Dr. Stalker]

I always thought that the number of stereoisomers for a compound could be calculated from 2^n, where n was the number of chiral centers.

I was taught that a chiral center was a carbon with 4 unique substituents, but according to this website, carbons with only 3 unique substituents are included?

Illustrated Glossary of Organic Chemistry - Stereocenter (chiral center)

Is this wrong?

A stereocenter isn't always a chiral center. Check the following links:

Stereochemistry

https://www.quora.com/What-is-the-difference-between-a-stereocenter-and-a-chiral-center

 

[rabbott1971]

I think the 2^n rule is good, and I didn't see where your link disputed it. As far as chiral centers with three bonds, I believe sometimes the lone pair can operate as a fourth substituent. Although there is rapid interconversion of the stereochemistry (the lone pair flips back and forth) there are situations where bonds to other structures can stabilize the chiral atom with three bonds and a lone pair, such that it displays enduring chirality. Please keep checking on your own, and let me know what you find out!

 

[aldol16]

I think the 2^n rule is good, and I didn't see where your link disputed it. As far as chiral centers with three bonds, I believe sometimes the lone pair can operate as a fourth substituent. Although there is rapid interconversion of the stereochemistry (the lone pair flips back and forth) there are situations where bonds to other structures can stabilize the chiral atom with three bonds and a lone pair, such that it displays enduring chirality. Please keep checking on your own, and let me know what you find out!

Yes, this is correct. One of the most commonly overlooked cases are amines. Amines can be chiral if there are three different substituents on the nitrogen. So if you have a molecule with a chiral center and an amine with three different substituents, then you may see distinguishable peaks on NMR corresponding to diastereomers. However, it's just about impossible to separate the amine enantiomers because the barrier to inversion is super low.