How do we know if this following molecule is Super Imposable mirror image or Non Super Imposable mirror image ? [See Image attached]


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    $\begingroup$ How do you know your left and right hands are not superimposable? (Or maybe they are?) $\endgroup$ – Ivan Neretin Apr 30 '19 at 10:38
  • $\begingroup$ Yes they are super imposable ? Because if we keep the mirror image of right hand on right hand , it's the same . $\endgroup$ – Nityoday Tekchandani Apr 30 '19 at 11:00
  • $\begingroup$ Super impossable mirror images means 2 mutualy mirror images, where you can identify one such an image with the other by its translation and rotation. Involve your imagination. $\endgroup$ – Poutnik Apr 30 '19 at 11:13
  • $\begingroup$ @Nityoday Tekchandani No, left and right hands are not super impossbale. You cannot formally by a geometry way identify the left(right) hand and its mirror image right(left), implying there is a mirror symmetry. $\endgroup$ – Poutnik Apr 30 '19 at 11:17
  • $\begingroup$ Okay, so according to what I understood, that a real object and it's mirror image, if they look same , they are super imposable , else non super imposable ? Also, then the question's answer would be Super Imposable ? $\endgroup$ – Nityoday Tekchandani Apr 30 '19 at 11:30
  • Take 2 round, soft objects like potatoes or apples.
  • Pin into each 4 pins of 3 different kinds ( 1 + 2 + 1 ),
    pointing to the most different directions.
  • Call the 1st pin bromine, the 2nd one hydrogen, the 3rd one ethyl.
  • Do the same for the other potato to be the mirror image of the first one.
  • Try to rotate one of them to look like the other.
  • If you succeed, they are superimposable.
  • Now, replace one of the same pins on both objects by another - 4th kind - of pins in such a way that they are still mutual mirror images.
  • Try to match them the same way you tried previously.
  • If you succeed, they are superimposable.

The summary:

  • While there are 2 hydrogen atoms on a carbon atoms - or more generally, there are only 3 kinds of groups on a C atom - the groups/atoms of the same kind are interchangeble and you can rotate the molecule to match the mirror image.
  • If there are 4 different groups on C atoms, you cannot make such a match.
  • Said by other way, the former case has a plane of symmetry, the latter case does not.
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  • $\begingroup$ Can we rotate the mirror image in x,y,z all the directions ? $\endgroup$ – Nityoday Tekchandani Apr 30 '19 at 11:33
  • $\begingroup$ Do you have in mind any reason why we cannot ? Imagine 2 pieces of LEGO. How would you determine they are identical ? You rotate them all the ways until you see they are the same - or not. $\endgroup$ – Poutnik Apr 30 '19 at 11:38
  • $\begingroup$ Okay, I tried this , $\endgroup$ – Nityoday Tekchandani Apr 30 '19 at 12:03
  • $\begingroup$ Step one : m.imgur.com/gallery/1cLeqQd Step two : m.imgur.com/gallery/Zyy2xfx I can successfully rotate the mirror image to get it like the first one !! Hence I've come to a conclusion that these are super Imposable. Am I correct ? $\endgroup$ – Nityoday Tekchandani Apr 30 '19 at 12:05
  • $\begingroup$ for some reasons I cannot get the images. but if you talk about the fiirst 1+2+1 case, you are correct. $\endgroup$ – Poutnik Apr 30 '19 at 12:08

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