How can the compound 1,2-cyclopentanediol have 3 stereoisomers? Isn't the configuration of the OH groups fixed in a ring?


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    $\begingroup$ The question here is not whether the configuration will change but what are all the possible stereoisomers (hypothetically) and why there are 3 of them. $\endgroup$ – SteffX Jul 31 '16 at 14:50

By definition, stereoisomers are the compounds which have same connectivity of atoms but different spacial orientation of atoms and two stereoisomers do not have same orientation from any point of view. There are different possibilities can a molecule of cylclopentane-1,2-diol can have: For simplicity, I have made two hydroxyl ($\ce{OH}$) into two methyl groups. But by definition you can cross out two structures because there exist a vantage point from which two molecules look the same (rotate molecule 180 out of plane and then rotate it slightly in plane, you get 2 pairs of identical molecules i.e 1,4 and 2,3. Hence, there are only two stereoisomers possible for cylopentane-1,2-diol. Hope that helps.

  • $\begingroup$ There are three stereoisomers. The meso compound and two enantiomers. $\endgroup$ – Lighthart Jul 31 '16 at 15:54
  • $\begingroup$ Yes, you are right Lighthart. I checked, meso compounds are stereoisomers. $\endgroup$ – jaspreet Jul 31 '16 at 19:58
  • $\begingroup$ Please do not answer questions that are closed/marked as duplicate. $\endgroup$ – Todd Minehardt Aug 1 '16 at 2:03
  • $\begingroup$ It was answered before it was closed or marked as duplicate $\endgroup$ – Lighthart Aug 2 '16 at 5:42

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