How many chiral centers and different stereoisomers ...

[Perseverance7779311]

How many chiral centers and different stereoisomers does 1,3-dimethylcyclohexane have? This is a Kaplan q bank question. The answer is 2 chiral centers and 3 stereoisomers. Could someone please explain why? Thanks.

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[aldol16]

Meso compounds.

 

[lakertodoc]

why wouldn't it be 4 stereoisomers?

R, R
R, S
S, R
S, S

?

 

[aldol16]

why wouldn't it be 4 stereoisomers?

R, R
R, S
S, R
S, S

Meso compounds.

 

[Dirtybird]

R, R and S, S are the same molecule.

 

[lakertodoc]

Okay so I was given the formula for number of stereoisomers is 2^n where n = # of chiral centers.

So the takeaway is I should be careful looking for symmetry. Is there anything else to be careful looking for when using this formula?

 

[Dirtybird]

Sounds like that's a good strategy (keeping an eye for symmetry). I had a hunch that the cis forms of this compound might be identical and drew it out real quick to confirm. Remember that meso = mirror image is superimposable; flip the mirror image 180 and it's the same molecule.

Is there anything else to be careful looking for when using this formula?

You can also have 0 chiral centers in a molecule with an alkene yet have 2 stereoisomers (Z and E forms).

 

[lakertodoc]

You rock, thanks @Dirtybird !