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I have heard that a conformational landscape encompasses all conformers that a compound has for a specific stereoisomer. I think it makes sense verbally, because if all conformers of a stereoisomer include all conformers for all stereoisomers and one (mistakenly) designates those all stereoisomer conformations to be conformers for a specific stereoisomer, it will require an interconversion (or change in permutational position) of one or multiple bonds to be broken to make a different stereoisomer.

While it seems to make verbal sense to me, my visual thinking is really against this. Searching on Google, "stereoisomer conformation" and "conformer" are always treated as two different realms having no connection in between.

I feel there should be an image (or someone has done a research article about this) showing a conformational landscape with a functional group bonded to a particular atom, showing differences in spatial 3D position. It suffices to show that "this coordinate position is still the same stereoisomer" but that if the functional group is extended, whether freely translated or rotated in drawing to somewhere, it will make a different stereoisomer and it is convincing enough that its stereochemistry interconversion will have to break some bonds first.

Any example would be fine, but I prefer the case of cis-trans conversion of a cyclohexane in its chair conformation with few functional groups, because my visualization is that its functional group stereochemistry interconversion still does not need bond breaking (but why it would have a different stereoisomer though?).

Thus, here is the general question. What is the extent or limit of conformational space of a molecule (or specifically, a particular stereoisomer) that is spatially unique to it, but if further extended to all random positional permutations will change its stereochemistry so that it will have to break some bonds first to let that interconversion happen?

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    $\begingroup$ How about being less verbose and maybe write something that is clear and specific? $\endgroup$
    – Mithoron
    Commented Dec 9, 2022 at 14:30
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    $\begingroup$ Also it's a bad example. Butene is good, even blatant, one. $\endgroup$
    – Mithoron
    Commented Dec 9, 2022 at 14:32
  • $\begingroup$ I want to know more about this though, this is important in stereochemistry education. +1 for you. $\endgroup$
    – làntèrn
    Commented Dec 9, 2022 at 16:56
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    $\begingroup$ It would definitely help if you were more concise and provided the simplest example of the problem you are facing. Try to use more punctuation (shorter and clearer sentences). It appears that this is about nomenclature, and specifically the meaning of the word "conformation". If so, a brief answer would be that it depends on context. $\endgroup$
    – Buck Thorn
    Commented Dec 9, 2022 at 16:57
  • $\begingroup$ @Mithoron What makes you think a butene is a better example than the author given even it is just a sitting planar that doesn't make any prominent conformational space. $\endgroup$
    – làntèrn
    Commented Dec 9, 2022 at 16:58

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You have the right idea that conformational space can be partitioned by configurational isomers. The clearest cases are where you have to break bonds to end up with another configurational isomer, but that is actually not always the case. Atropisomerism also gives rise to different configurational isomers, even though they are just separated by a bond rotation with a very high barrier.

Your example with cyclohexane is actually a clear-cut case, since you really need to break bonds to switch from cis to trans. I visualized all possible chair conformations and the partitioning into configurational subspaces. There are more conformers that I left out for simplification.

Conformational space partitioning for cyclohexane-1,2-d2

If you still don't see why you need bond breaking, I recommend playing around with a molecular model kit.

In summary, the partitioning of conformers into distinct configurational isomers happens when they are interconverted by a process with a high barrier (i.e. bond breaking, hindered rotations, polytopal rearrangements, etc.).

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  • $\begingroup$ I will edit the comment a bit while writing. $\endgroup$
    – Leticia
    Commented Dec 10, 2022 at 4:17
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    $\begingroup$ I get it now. Thank you very much for clearing up and sharing this. Seems like I got the wrong terminology classification then (as you noted in the question's comment). Let me conclude this. So, a molecule has a global stereoisomer space (not a global conformational space) that can be partitioned into whether the interconversion of this space permutation will make a different configuration (configurational space, not stereochemical space) or not (conformational space). $\endgroup$
    – Leticia
    Commented Dec 10, 2022 at 5:01
  • $\begingroup$ The configurational space can be generated by some processes that the bond breaking process is not always a sole requirement to make a different configuration because it can be interconverted by another process requiring high barrier i.e. a hindered rotation to make atropisomers. I believe enzymatic catalysis performs this more commonly than the frequency it mentioned in the textbooks though. $\endgroup$
    – Leticia
    Commented Dec 10, 2022 at 5:02
  • $\begingroup$ Thank you very much for sharing this. The chair conformations in each configurational subspaces of cis and trans configurations are aesthetically pleasing to me as I can imagine with the given equlibrium arrows. I will affirm it later with my slo-mo molecular dynamics simulation to see each process. Again, thank you very much. $\endgroup$
    – Leticia
    Commented Dec 10, 2022 at 5:02
  • $\begingroup$ By the way, where do you obtain the picture? The link you gave is quite a bit different source one $\endgroup$
    – Leticia
    Commented Dec 10, 2022 at 5:30

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