5.5 How to Identify Type of Isomerism | Organic Chemistry

Chad shows how to identify the type of isomerism between two molecules if any. They may be different compounds, identical, constitutional isomers, enantiomers, or diastereomers. The first question to ask is whether two molecules even have the same bond connectivity as this will help determine between constitutional isomers and stereoisomers. If two molecules do not have the same bond connectivity, they are either constitutional isomers or not even isomers at all. If two molecules have the same bond connectivity, they are either identical, enantiomers, or diastereomers (i.e. identical or stereoisomers).

Chad demonstrates that in some cases the pair of molecules may be drawn in such a way that the visual comparison is all that is needed to identify the type of isomerism. In other cases, a visual comparison may be problematic, and he shows that assigning R and S to chiral centers can help to distinguish between structures that have the same bond connectivity. In such cases, if the two molecules have all the same absolute configurations (same assignments of R and S), then they are identical. If they are chiral and have all the opposite absolute configurations, they are enantiomers. Finally, if they have some chiral centers in the same configuration and some in the opposite configuration, then they are diastereomers.

00:00 Lesson Introduction
01:01 Problem #1 - Identical, Enantiomers, or Diastereomers?
03:28 Problem #2 - Identical, Enantiomers, or Diastereomers?
05:49 Problem #3 - Identical, Enantiomers, or Diastereomers?
08:44 Problem #4 - Meso Compound - Identical?
10:04 Problem #5 - Identical, Enantiomers, or Diastereomers with Fischer Projections

[LuckyYouDude]

You are amazingly good at teaching. I have been gobbling up these OChen videos faster I can say OChem. Then I saw your Physics videos, man, am I lucky taking both these classes and getting help from best teacher on these subjects. Thank you so much for these videos. You are on another level when it comes to delivering these complex topics. Thank you again!

[sabinamaria]

Thank you so much for these videos!!They have led me from hating organic chem to actually enjoying it, due to your easy understandable teaching methods.

[MarkTrujillo-lr]

Is it because Fischer Projections are not an actual 3-D representation of the molecule that we do not identify that there is an internal mirror image for the molecule on the left 10:05
Thank you again for all of your help!!!

[ilovecows]

how were the first ones not constitutional isomers? dont they have different bond connectivity?

[SavannaStanley-mo]

baaaack at it again w the percentage boost in ochem, thank you again chad!!! wouldnt make it without u

[RazaUllah-tx]

Thank you for the amazing teaching content. However, one of the structures of 1, 2, 3, 4-butanetetrol you have drawn on the board is a meso compound, and meso compounds are achiral, but diastereomers are chiral compounds. So how do these two structures have a diastereomeric relationship? If I am wrong, please, correct it. Thank you very much.

[SuzannesTutoring]

This is so helpful! I was confused about diastereomers before and this cleared it up for me!
I may be overthinking this, but if mirror images of an achiral compound are, by definition, superimposable... then wouldn't they just be identical? What's the difference between 2 superimposable mirror images of an achiral compound and 2 different drawings of the exact same compound? Or maybe achiral compounds' mirror images ARE identical compounds? Am I close? ;-)

[flaffy]

At 9:22 how are those chiral centers when the two carbons they bind to are exactly the same?

[ayeshaarslan]

Can you please explain what the line on top of Ch3's is? I haven't seen it before anywhere

[nonspeedy]

At 5:44, if the two compounds both had an S chiral center, would that make the molecules identical or diastereomers?

[ufcbrotha]

do planes of symmetry not matter on fischer projections? asking for example 5, compound on the left has a plane of symmetry but considering we altered it I dont think it matters, but just checking

[NoorNoor-pfid]

Is there a quick trick on the exam to determine which type they are? For example, when you said if you have one chiral center, you will be considered chiral automatically. I have my final this upcoming Wednesday and I'm watching your videos for a refresher on this semester's material. Thank you.

[زهرافرخزاده]

It was really helpfull, thank you chad❤

[QuickSilver]

Why isn't the fourth example constitutional isomers? The connectivity of which Carbons the Cl's are attached to are different between the molecules. For it to be meso, wouldn't the Cl's need to be on the right side?

[sirehsy]

sorry but in the last example, Wasn't one of them meso? the left one ?

[anika]

i love u chad and ur bald head. ur awesome💞💞💞💞💞💞