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I am currently struggling on seeing where exactly conformational isomers fit within stereochemistry & how (and whether) they are a subset of diasteromers. I've seen potentially conflicting information online on the definition of diasteromers (some sources mention that diasteromers are not mirror images of each other and not superimposable, while others don't explicitly mention the superimposable part).

I am convinced that enantiomers and geometric (cis-trans) isomers are a type of configurational isomer, the latter a subset of diasteromers (I hope this is correct), since they require bonds to break in order be superimposed with each other. However, due to some online sources differing in their mentioning of the superimposability requirement of diasteromers, I'm not sure whether diasteromers are a subset of configurational isomers (if this is the case, then it would seem incorrect to place conformational isomers within diasteromers, since it itself is a subset of configurational isomers).

For more of a visual explanation, see the below flowcharts:

(a) First flowchart; conformational isomers / conformers within diasteromers category. Doesn't mention configurational isomers & where they fit in.

(from Wikipedia)First flowchart

(b) Second flowchart; conformational isomers is outside the stereoisomer category. I assume that optical isomers are a subset of configurational isomers? Second flowchart

(From LibreTexts)

(c) This flowchart separates configurational and conformational isomers and places diasteromers under configurational isomers. I feel that this third flowchart most closely resembles how I would personally organize all of the isomers (the only thing I'm unsure about is the mention of optical isomers, which I assume is a quality all non-cis-trans/geometric isomers exhibit). Third flowchart

(from the University of Cagalry)

Any help on this would be greatly appreciated! Thank you so much :)

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  • $\begingroup$ The last flow chart should include identical molecules (they have the molecular formula, so they are part of the main branch). $\endgroup$
    – Karsten
    Sep 28, 2023 at 20:26

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Conformational isomers as in (boat vs chair for rings or s cis vs s trans for dienes or what the flowchart describes as rotamers) are not diastereomers, or any time of isomers strictly.

Conformational isomers are identical molecules, just in different momentary positions. Any two conformational isomers will be rapidly inter converting between each other and are impossible to isolate.

They only become significant when thinking about why a reaction can lead to different stereo chemical products. E.g. E2 eliminations that lead to cis vs trans isomers- here the difference in product is due to the reactant molecules being in different conformations when they reacted.

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