Number of Stereoisomers in a Cyclic Molecule? (what the heck!)

[manohman]

The question asks for the total number of possible stereoisomers. (question below)

Normally when you have a stereocenter that is attached to a ring you still count the 2 stereoisomers that arise from that stereocenter. Why is it different in this case?

The explanation says (shown below) that because of the cyclic nature of the molecule, not all stereocenters can be inverted.
But then why is are there 2 possibilities then? If you cant switch anything around, wouldn't it just be 1 stereoisomer?

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[Cawolf]

It is weird, because generally you think 2^n - which is the maximum number of stereoisomers.

There are 2 isomers because the mirror image can exist - so you have one pair of enantiomers.

The bicyclic configuration limits your ability to swap just one group and form the diastereomers.

 

[manohman]

I see. So when the stereocenter is where two carbon rings branch from, you cannot interchange the bonds due to the structure.

That makes a lot of sense thanks man!

 

[Cawolf]

No problem.

There is no hard and fast rule though so be careful. In this particular case the structure limits the stereochemistry.

 

[chemtopper]

The question asks for the total number of possible stereoisomers. (question below)

Normally when you have a stereocenter that is attached to a ring you still count the 2 stereoisomers that arise from that stereocenter. Why is it different in this case?

The explanation says (shown below) that because of the cyclic nature of the molecule, not all stereocenters can be inverted.
But then why is are there 2 possibilities then? If you cant switch anything around, wouldn't it just be 1 stereoisomer?

The given stereo isomer has only one more stereo isomer and they are non super imposable mirror images enantiomer.