Here are some practice questions about isomerism.

1) PtCl₂(NO₂)₂(NH₃)₂ has 5 diastereomers and one of them has an enantiomer. Draw them.

1) Draw the facial and meridional isomers of CoBr₃(OH₂)₃. Are either of these chiral molecules?

Neither of these molecules are chiral. They both have mirror planes (Can you find them?)

2) Are these molecules chiral?

No, it has a mirror plane. (The plane includes the NO₂ ligand and reflects the Cl onto the Cl and the Br onto the Br.)

No, it has a mirror plane. (The plane includes the Br ligand and the chloride ligand pointing into the page. It reflects the Cls onto each other.)

Yes, it is chiral because it doesn’t have a mirror plane or an inversion centre (or an improper axis of rotation). Prove this to yourself by drawing the mirror image and trying to rotate one enantiomer to superimpose it on the other. No matter how you rotate it, you won’t be able to superimpose the two images.

Yes, it is chiral. Try to draw the mirror image and superimpose it on the original.

No, it has a mirror plane that includes the Br and the NO₂ can reflects the two acac ligands onto one another. It might be easier to see if you draw the molecule rotated with the two rings in the equatorial plane and the other ligands axial. (Acac ligands show resonance, so don’t worry about where the double bonds are when you reflect it.)

4. Name the chiral complexes (D or L)

Hint: Use the same approach as for tris-chelate complexes (ones with three-rings)