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

Ethanol "isomers"

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    $\begingroup$ If ethanol was flat, it would make sense, but it isn't. $\endgroup$ – Mithoron Mar 3 '16 at 12:29
  • $\begingroup$ They can be stereo isomers instead. See upload.wikimedia.org/wikipedia/commons/thumb/1/11/… for 3d structure of ethanol. $\endgroup$ – another 'Homo sapien' Mar 3 '16 at 12:33
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    $\begingroup$ If ethanol was static, this would be true, but it isn't. $\endgroup$ – jerepierre Mar 3 '16 at 16:12
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    $\begingroup$ 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 Mar 3 '16 at 22:17

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 Jan 2 '18 at 14:19
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    $\begingroup$ @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. $\endgroup$ – Martin - マーチン Jan 2 '18 at 23:16

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