if you are asked to draw the stereoisomers of a cyclopropane with one chloro- and one bromo- subsstituent?

Question

then give the correct name for each isomer, can more than one of your isomers have the same name and can you place the Cl and Br on the same Carbon atom?

Answer 1

There is only one isomer for a mono subsituted cyclopropane. If you build the model and twist it all you like, you will never get that chlorine atom to be cis or trans - it will alway be cis.

As far as putting two atoms on the ring, sure it's ok to do that if that is what you are allowed to do - again - there would only be ONE isomer of it!

Answer 2

Moving either the Cl or Br to a different C atom makes a different structural isomer, not a stereoisomer.

Of course there will an isomer with the Br and Cl on the same C atom, but it won't have stereoisomers.

The question is basically about you recognising that there are cis and trans isomers, and that the trans isomer is optically active.

Answer 3

The correct name for the molecule in question is 1-bromo-2-chlorocyclopropane.
There are 2 stereocenters. Remember that a molecule with n stereocenters has 2^n stereoisomers.
The possible isomers are (1R, 2R)-, (1S, 2R)-, (1S, 2S)-, and 1R, 2S)-1-bromo-2-chlorocyclopropane.
1-bromo-1-chlorocyclopropane is achiral, so there are no stereoisomers of this molecule.