[msohn88]

My question is about stereo chemistry.

When you draw cis-1,3,-dimethylcyclobutane.

For me, it has different mirror images, but it says it's identical mirror images.

I just don't see how it works... I know it's superimposable, but but I don't think that has to do with something.

Could Anybody explain to me clearly? Please?

[taurean]

My question is about stereo chemistry.

When you draw cis-1,3,-dimethylcyclobutane.

For me, it has different mirror images, but it says it's identical mirror images.

I just don't see how it works... I know it's superimposable, but but I don't think that has to do with something.

Could Anybody explain to me clearly? Please?

It has plane of symmetry passing through the C atoms attached to the methyl groups.  So, its achiral.

[msohn88]

It has plane of symmetry passing through the C atoms attached to the methyl groups.  So, its achiral.

I don't know what you mean by "plane of symmetry passing through the C atoms...".

Could you make it simpler?

[taurean]

It has plane of symmetry passing through the C atoms attached to the methyl groups.  So, its achiral.

I don't know what you mean by "plane of symmetry passing through the C atoms...".

Could you make it simpler?

Here is the picture. The presence of plane of symmetry (a mirror plane which divides the molecule into two equal halves) makes the molecule achiral.

[msohn88]

It has plane of symmetry passing through the C atoms attached to the methyl groups.  So, its achiral.

I don't know what you mean by "plane of symmetry passing through the C atoms...".

Could you make it simpler?

Here is the picture. The presence of plane of symmetry (a mirror plane which divides the molecule into two equal halves) makes the molecule achiral.

Oh! so, if it has symmetry and divides the molecule into two equal halves, that means it's achiral, and if not, it's chiral and enantimoers!

Thank you very much!

[spirochete]

What taurean said is 100% true, but I just wanted to emphasize also that an achiral molecule is always superimposable on its mirror image. 

The visualization involved in doing this can be extremely tricky though, because often you have to rotate the molecule before it can be superimposable.  In the end it's perfectly fine if you can only fine the plane of symmetry.  This is all you need to know that a molecule is achiral.

[Ahmed Abdullah]

I think trans-1,3,-dimethylcyclobutane is chiral.

[azmanam]

I think trans-1,3,-dimethylcyclobutane is chiral.

nope.  Still has a plane of symmetry.  Also, remember what you need for a chiral atom: 4 different groups.  If you look at one of the carbon atoms the 4 groups are: H, CH₃, CH₂-CH(CH₃), CH₂-CH(CH₃).  The group going around the ring in one direction is exactly the same as the group going around the ring in the other direction. You do not have 4 different groups.  Therefore you do not have a chiral atom.

If it was trans-1,3-dimethylcyclopentane, then it's chiral.

[winterwind]

Also keep in mind that just because you cannot find a plane of symmetry doesn't mean the molecule is necessarily chiral.