Are the two structures depicting the same molecule? Why? Why not?

Ethanol "isomers"

  • 9
    $\begingroup$ If ethanol was flat, it would make sense, but it isn't. $\endgroup$
    – Mithoron
    Commented Mar 3, 2016 at 12:29
  • $\begingroup$ They can be stereo isomers instead. See upload.wikimedia.org/wikipedia/commons/thumb/1/11/… for 3d structure of ethanol. $\endgroup$ Commented Mar 3, 2016 at 12:33
  • 2
    $\begingroup$ If ethanol was static, this would be true, but it isn't. $\endgroup$
    – jerepierre
    Commented Mar 3, 2016 at 16:12
  • 1
    $\begingroup$ There could be atropoisomers if rotation was blocked but it would need very low temperature to try to separate what is normally rotamers of ethanol. $\endgroup$
    – Mithoron
    Commented Mar 3, 2016 at 22:17

1 Answer 1


Try to imagine it in a 3D fashion. You can look it at molcalc.org. The molecule rotates around the $\ce{C-C}$ bond converting one structure into the other. These rotations are very fast.

Another point is, that the representations you chose are 2D, so the could still represent the same molecule:

same molecule different angles

  • $\begingroup$ I changed the URL for ethanol model, the previous one gives error 404 (probably they change the part in the address that looks like a hash from time to time). $\endgroup$
    – andselisk
    Commented Jan 2, 2018 at 14:19
  • 1
    $\begingroup$ @andselisk thanks. Maybe I should come back to this again and add an animated gif, or even link to some other provider as a backup. The Pittsburgh repository comes to mind, but I guess that was still in its infancy when writing this answer. $\endgroup$ Commented Jan 2, 2018 at 23:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.