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When I searched the stereoisomers of 1,3,5-trimethylcyclohexane, I got four structures given below.

stereoisomers of 1,3,5-trimethylcyclohexane

I don't get how structures 1 and 2, 3, and 4 are not the same. Could anyone explain?

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    $\begingroup$ 1 and 2 are the same all right. $\endgroup$ Jan 30, 2022 at 13:19
  • $\begingroup$ @IvanNeretin what about 3 and 4 how are they different if we just turn the ring upside down? $\endgroup$
    – L lawliet
    Jan 30, 2022 at 13:23
  • $\begingroup$ They aren't different either. $\endgroup$ Jan 30, 2022 at 13:28

1 Answer 1

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1,3,5-Trimethylcyclohexane doe not show optical isomerism as it has no chiral carbon atoms. Therefore, we are left with counting the total number of cistrans isomers.

1,3,5-Trimethylcyclohexane has two cistrans isomers which are given by structures 1 and 3 in your diagram.

1 and 2 are identical because if you look from behind the plane of the screen, 1 will turn into 2. Similar argument holds for 3 and 4. Hence we get two distinct cistrans isomers.

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  • $\begingroup$ They are conformational isomers e,e,e and a,a,a and a,e,e and e,a,a. So it depends on temperature. Molecules are 3-dimensional. $\endgroup$
    – jimchmst
    Sep 9, 2023 at 18:36

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